In Internet slang, a troll ( / / , / / ) is a person who sows discord on the Internet by starting arguments or upsetting people, by posting inflammatory,  extraneous, or off-topic messages in an online community (such as a newsgroup, forum, chat room, or blog) with the deliberate intent of provoking readers into an emotional response  or of otherwise disrupting normal on-topic discussion,  often for their own amusement.
This sense of the word "troll" and its associated verb trolling are associated with Internet discourse, but have been used more widely. Media attention in recent years has equated trolling with online harassment. For example, mass media has used troll to describe "a person who defaces Internet tribute sites with the aim of causing grief to families."   In addition, depictions of trolling have been included in popular fictional works such as the HBO television program The Newsroom , in which a main character encounters harassing individuals online and tries to infiltrate their circles by posting negative sexual comments himself.
Application of the term troll is subjective. Some readers may characterize a post as trolling , while others may regard the same post as a legitimate contribution to the discussion, even if controversial. Like any pejorative term, it can be used as an ad hominem attack, suggesting a negative motivation.
As noted in an OS News article titled "Why People Troll and How to Stop Them" (25 January 2012), "The traditional definition of trolling includes intent. That is, trolls purposely disrupt forums. This definition is too narrow. Whether someone intends to disrupt a thread or not, the results are the same if they do."  Others have addressed the same issue, e.g., Claire Hardaker, in her Ph.D. thesis "Trolling in asynchronous computer-mediated communication: From user discussions to academic definitions",  and Dr. Phil. Popular recognition of the existence (and prevalence) of non-deliberate, "accidental trolls", has been documented widely, in sources as diverse as Nicole Sullivan's keynote speech at the 2012 Fluent Conference, titled "Don't Feed the Trolls"  Gizmodo,  online opinions on the subject written by Silicon Valley executives  and comics. 
Regardless of the circumstances, controversial posts may attract a particularly strong response from those unfamiliar with the robust dialogue found in some online, rather than physical, communities. Experienced participants in online forums know that the most effective way to discourage a troll is usually to ignore it, because responding tends to encourage trolls to continue disruptive posts – hence the often-seen warning: "Please do not feed the trolls".
At times, the word can be abused to refer to anyone with controversial opinions they disagree with.  Such usages goes against the ordinary meaning of troll in multiple ways. Most importantly, trolls don't actually believe the controversial views they claim. Farhad Manjoo criticises this view, noting that if the person really is trolling, they are a lot more intelligent than their critics would believe. 
Origin and etymology
The English noun troll in the standard sense of ugly dwarf or giant dates to 1610 and comes from the Old Norse word troll meaning giant or demon.  The word evokes the trolls of Scandinavian folklore and children's tales: antisocial, quarrelsome and slow-witted creatures which make life difficult for travellers.  
In modern English usage, trolling may describe the fishing technique of slowly dragging a lure or baited hook from a moving boat  whereas trawling describes the generally commercial act of dragging a fishing net. Early non-Internet slang use of trolling can be found in the military: by 1972 the term trolling for MiGs was documented in use by US Navy pilots in Vietnam. It referred to use of "...decoys, with the mission of drawing...fire away..." 
The contemporary use of the term is alleged to have appeared on the Internet in the late 1980s,   but the earliest known attestation according to the Oxford English Dictionary is in 1992.  
The context of the quote cited in the Oxford English Dictionary  sets the origin in Usenet in the early 1990s as in the phrase "trolling for newbies", as used in alt.folklore.urban (AFU).   Commonly, what is meant is a relatively gentle inside joke by veteran users, presenting questions or topics that had been so overdone that only a new user would respond to them earnestly. For example, a veteran of the group might make a post on the common misconception that glass flows over time. Long-time readers would both recognize the poster's name and know that the topic had been discussed a lot, but new subscribers to the group would not realize, and would thus respond. These types of trolls served as a practice to identify group insiders. This definition of trolling, considerably narrower than the modern understanding of the term, was considered a positive contribution.   One of the most notorious AFU trollers, David Mikkelson,  went on to create the urban folklore website Snopes.com.
By the late 1990s, alt.folklore.urban had such heavy traffic and participation that trolling of this sort was frowned upon. Others expanded the term to include the practice of playing a seriously misinformed or deluded user, even in newsgroups where one was not a regular; these were often attempts at humor rather than provocation. The noun troll usually referred to an act of trolling—or to the resulting discussion—rather than to the author, though some posts punned on the dual meaning of troll. 
In other languages
In Chinese, trolling is referred to as bái mù ( Chinese: 白目 ; literally: "white eye"), which can be straightforwardly explained as "eyes without pupils", in the sense that whilst the pupil of the eye is used for vision, the white section of the eye cannot see, and trolling involves blindly talking nonsense over the internet, having total disregard to sensitivities or being oblivious to the situation at hand, akin to having eyes without pupils. An alternative term is bái làn ( Chinese: 白爛 ; literally: "white rot"), which describes a post completely nonsensical and full of folly made to upset others, and derives from a Taiwanese slang term for the male genitalia, where genitalia that is pale white in colour represents that someone is young, and thus foolish. Both terms originate from Taiwan, and are also used in Hong Kong and mainland China. Another term, xiǎo bái ( Chinese: 小白 ; literally: "little white") is a derogatory term that refers to both bái mù and bái làn that is used on anonymous posting internet forums. Another common term for a troll used in mainland China is pēn zi ( Chinese: 噴子 ; literally: "sprayer, spurter").
In Japanese, tsuri ( 釣り ) means "fishing" and refers to intentionally misleading posts whose only purpose is to get the readers to react, i.e. get trolled. arashi ( 荒らし ) means "laying waste" and can also be used to refer to simple spamming.
In Korean, nak-si (낚시) means "fishing", and is used to refer to Internet trolling attempts, as well as purposefully misleading post titles. A person who recognizes the troll after having responded (or, in case of a post title nak-si , having read the actual post) would often refer to himself as a caught fish.
In Portuguese, more commonly in its Brazilian variant, troll (produced [ˈtɾɔw] in most of Brazil as spelling pronunciation) is the usual term to denote internet trolls (examples of common derivate terms are trollismo or trollagem , "trolling", and the verb trollar , "to troll", which entered popular use), but an older expression, used by those which want to avoid anglicisms or slangs, is complexo do pombo enxadrista to denote trolling behavior, and pombos enxadristas (literally, "chessplayer pigeons") or simply pombos are the terms used to name the trolls. The terms are explained by an adage or popular saying: "Arguing with fulano (i.e., John Doe) is the same as playing chess with a pigeon: the pigeon defecates on the table, drop the pieces and simply fly, claiming victory."
In Thai, the term krian ( เกรียน) has been adopted to address Internet trolls. According to the Royal Institute of Thailand, the term, which literally refers to a closely cropped hairstyle worn by schoolboys in Thailand, is from the behaviour of these schoolboys who usually gather to play online games and, during which, make annoying, disruptive, impolite, or unreasonable expressions. The term top krian (ตบเกรียน; "slap a cropped head") refers to the act of posting intellectual replies to refute and cause the messages of Internet trolls to be perceived as unintelligent.
In the Sinhala language, this is called ala kireema (අල කිරීම), which means "Turning it into Potatoes (Sabotage)". Sometimes it is used as ala vagaa kireema (අල වගා කිරීම)—"Planting Potatoes". People/Profiles who does trolling often are called "Potato Planters"— ala vagaakaruvan (අල වගාකරුවන්). This seems to be originated from university slang ala væda (අල වැඩ) which means "Potato business" is used for breaking the laws/codes of the university.
Trolling, identity, and anonymity
Early incidents of trolling  were considered to be the same as flaming, but this has changed with modern usage by the news media to refer to the creation of any content that targets another person. The Internet dictionary NetLingo suggests there are four grades of trolling: playtime trolling, tactical trolling, strategic trolling, and domination trolling.  The relationship between trolling and flaming was observed in open-access forums in California, on a series of modem-linked computers. CommuniTree was begun in 1978 but was closed in 1982 when accessed by high school teenagers, becoming a ground for trashing and abuse.  Some psychologists have suggested that flaming would be caused by deindividuation or decreased self-evaluation: the anonymity of online postings would lead to disinhibition amongst individuals  Others have suggested that although flaming and trolling is often unpleasant, it may be a form of normative behavior that expresses the social identity of a certain user group  According to Tom Postmes, a professor of social and organisational psychology at the universities of Exeter, England, and Groningen, The Netherlands, and the author of Individuality and the Group , who has studied online behavior for 20 years, "Trolls aspire to violence, to the level of trouble they can cause in an environment. They want it to kick off. They want to promote antipathetic emotions of disgust and outrage, which morbidly gives them a sense of pleasure." 
The practice of trolling has been documented by a number of academics as early as the 1990s. This included Steven Johnson in 1997 in the book, Interface Culture, and Judith Donath in 1999. Donath's paper outlines the ambiguity of identity in a disembodied " virtual community " such as Usenet:
In the physical world there is an inherent unity to the self, for the body provides a compelling and convenient definition of identity. The norm is: one body, one identity ... The virtual world is different. It is composed of information rather than matter. 
Trolling is a game about identity deception, albeit one that is played without the consent of most of the players. The troll attempts to pass as a legitimate participant, sharing the group's common interests and concerns; the newsgroups members, if they are cognizant of trolls and other identity deceptions, attempt to both distinguish real from trolling postings, and upon judging a poster a troll, make the offending poster leave the group. Their success at the former depends on how well they – and the troll – understand identity cues; their success at the latter depends on whether the troll's enjoyment is sufficiently diminished or outweighed by the costs imposed by the group.
Trolls can be costly in several ways. A troll can disrupt the discussion on a newsgroup, disseminate bad advice, and damage the feeling of trust in the newsgroup community. Furthermore, in a group that has become sensitized to trolling – where the rate of deception is high – many honestly naïve questions may be quickly rejected as trollings. This can be quite off-putting to the new user who upon venturing a first posting is immediately bombarded with angry accusations. Even if the accusation is unfounded, being branded a troll is quite damaging to one's online reputation. 
Susan Herring and colleagues in "Searching for Safety Online: Managing 'Trolling' in a Feminist Forum" point out the difficulty inherent in monitoring trolling and maintaining freedom of speech in online communities: "harassment often arises in spaces known for their freedom, lack of censure, and experimental nature".  Free speech may lead to tolerance of trolling behavior, complicating the members' efforts to maintain an open, yet supportive discussion area, especially for sensitive topics such as race, gender, and sexuality. 
Corporate, political, and special interest sponsored trolls
Investigative journalist Sharyl Attkisson is one of several in the media who has reported on the increasing trend for organizations to utilize trolls to manipulate public opinion as part and parcel of an Astroturfing initiative. Teams of sponsored trolls, sometimes referred to as sockpuppet armies,   swarm a site to overwhelm any honest discourse and denigrate any who disagree with them.  A 2012 Pew Center on the States presentation on Effective Messaging included two examples of social media posts by a recently launched "rapid response team" dedicated to promoting fluoridation of community water supplies. That same presentation also emphasized changing the topic of conversation as a winning strategy.  A 2016 story in the Harvard Gazette reported that the Chinese government is estimated to produce over 400 million fake social media posts every year, in order to promote pro-government material. 
A 2016 study for the NATO Strategic Communications Centre of Excellence (NATO StratCom COE) on hybrid warfare notes that the Russian military intervention in Ukraine "demonstrated how fake identities and accounts were used to disseminate narratives through social media, blogs, and web commentaries in order to manipulate, harass, or deceive opponents."  (p3) The NATO report describes that a " Wikipedia troll" uses a type of message design where a troll does not add "emotional value" to reliable "essentially true" information in re-posts, but presents it "in the wrong context, intending the audience to draw false conclusions." For example, information, without context, from Wikipedia about the military history of the United States "becomes value-laden if it is posted in the comment section of an article criticizing Russia for its military actions and interests in Ukraine. The Wikipedia troll is 'tricky', because in terms of actual text, the information is true, but the way it is expressed gives it a completely different meaning to its readers."  (p62) Unlike "classic trolls," Wikipedia trolls "have no emotional input, they just supply misinformation " and are one of "the most dangerous" as well as one of "the most effective trolling message designs."  (pp70, 76) Even among people who are "emotionally immune to aggressive messages" and apolitical, "training in critical thinking " is needed, according to the NATO report, because "they have relatively blind trust in Wikipedia sources and are not able to filter information that comes from platforms they consider authoritative."  (p72) While Russian-language hybrid trolls use the Wikipedia troll message design to promote anti-Western sentiment in comments, they "mostly attack aggressively to maintain emotional attachment to issues covered in articles."  (p75) Discussions about topics, other than International sanctions during the Ukrainian crisis, "attracted very aggressive trolling" and became polarized according to the NATO report, which "suggests that in subjects in which there is little potential for re-educating audiences, emotional harm is considered more effective" for pro-Russian Latvian-language trolls.  (p76)
Two studies published in 2013 and 2014 have found that people who are identified as trolls tend to have dark personality traits and show signs of sadism, antisocial behavior, psychopathy, and machiavellianism.   The 2013 study suggested that there are a number of similarities between anti-social and flame trolling activities  and the 2014 study suggested that the noxious personality characteristics known as the " dark triad of personality" should be investigated in the analysis of trolling, and concluded that trolling appears "to be an Internet manifestation of everyday sadism."  Their relevance is suggested by research linking these traits to bullying in both adolescents and adults. The 2014 study found that trolls operate as agents of chaos on the Internet, exploiting hot-button issues to make users appear overly emotional or foolish in some manner. If an unfortunate person falls into their trap, trolling intensiﬁes for further, merciless amusement. This is why novice Internet users are routinely admonished, "Do not feed the trolls!" The 2013 study found that trolls often have a high expectation of what it means to be successful, which is higher than they are able to attain, and this results in them resenting others who think they are successful but who fall below their standards.
Researcher Ben Radford wrote about the phenomenon of clowns in history and modern day in his book Bad Clowns and found that bad clowns have evolved into Internet trolls. They do not dress up as traditional clowns, but for their own amusement, they tease and exploit "human foibles" in order to speak the "truth" and gain a reaction. Like clowns in make-up, Internet trolls hide behind "anonymous accounts and fake usernames." In their eyes they are the trickster and are performing for a nameless audience via the Internet.
A concern troll is a false flag pseudonym created by a user whose actual point of view is opposed to the one that the troll claims to hold. The concern troll posts in Web forums devoted to its declared point of view and attempts to sway the group's actions or opinions while claiming to share their goals, but with professed "concerns". The goal is to sow fear, uncertainty and doubt within the group. 
An example of this occurred in 2006 when Tad Furtado, a staffer for then-Congressman Charles Bass ( R - NH), was caught posing as a "concerned" supporter of Bass' opponent, Democrat Paul Hodes, on several liberal New Hampshire blogs, using the pseudonyms "IndieNH" or "IndyNH". "IndyNH" expressed concern that Democrats might just be wasting their time or money on Hodes, because Bass was unbeatable.   Hodes eventually won the election.
Although the term "concern troll" originated in discussions of online behavior, it now sees increasing use to describe similar behaviors that take place offline. For example, James Wolcott of Vanity Fair accused a conservative New York Daily News columnist of "concern troll" behavior in his efforts to downplay the Mark Foley scandal. Wolcott links what he calls concern trolls to what Saul Alinsky calls "Do-Nothings", giving a long quote from Alinsky on the Do-Nothings' method and effects:
These Do-Nothings profess a commitment to social change for ideals of justice, equality, and opportunity, and then abstain from and discourage all effective action for change. They are known by their brand, 'I agree with your ends but not your means'. 
The Hill published an op-ed piece by Markos Moulitsas of the liberal blog Daily Kos titled "Dems: Ignore 'Concern Trolls'". The concern trolls in question were not Internet participants but rather Republicans offering public advice and warnings to the Democrats. The author defines "concern trolling" as "offering a poisoned apple in the form of advice to political opponents that, if taken, would harm the recipient". 
While many webmasters and forum administrators consider trolls a scourge on their sites, some websites welcome them. For example, a New York Times article discussed troll activity at 4chan and at Encyclopedia Dramatica, which it described as "an online compendium of troll humor and troll lore".  4chan's /b/ board is recognized as "one of the Internet's most infamous and active trolling hotspots."  This site and others are often used as a base to troll against sites that their members can not normally post on. These trolls feed off the reactions of their victims because "their agenda is to take delight in causing trouble". 
Media coverage and controversy
Mainstream media outlets have focused their attention on the willingness of some Internet users to go to extreme lengths to participate in organized psychological harassment.
In February 2010, the Australian government became involved after users defaced the Facebook tribute pages of murdered children Trinity Bates and Elliott Fletcher. Australian communications minister Stephen Conroy decried the attacks, committed mainly by 4chan users, as evidence of the need for greater Internet regulation, stating, "This argument that the Internet is some mystical creation that no laws should apply to, that is a recipe for anarchy and the wild west."  Facebook responded by strongly urging administrators to be aware of ways to ban users and remove inappropriate content from Facebook pages.  In 2012, the Daily Telegraph started a campaign to take action against "Twitter trolls", who abuse and threaten users. Several high-profile Australians including Charlotte Dawson, Robbie Farah, Laura Dundovic, and Ray Hadley have been victims of this phenomenon.   
In the United Kingdom, contributions made to the Internet are covered by the Malicious Communications Act 1988 as well as Section 127 of the Communications Act 2003, under which jail sentences were, until 2015, limited to a maximum of six months.  In October 2014, the UK's Justice Secretary, Chris Grayling, said that "internet trolls" would face up to two years in jail, under measures in the Criminal Justice and Courts Bill that extend the maximum sentence and time limits for bringing prosecutions.   The House of Lords Select Committee on Communications had earlier recommended against creating a specific offence of trolling. Sending messages which are "grossly offensive or of an indecent, obscene or menacing character" is an offence whether they are received by the intended recipient or not.  Several people have been imprisoned in the UK for online harassment. 
Sean Duffy, who mocked the testimonial page of a dead teenager, was sentenced to eighteen weeks in prison and banned from using social networking sites for five years.  Trolls of the testimonial page of Georgia Varley faced no prosecution due to misunderstandings of the legal system in the wake of the term trolling being popularized.  In October 2012, a twenty-year-old man was jailed for twelve weeks for posting offensive jokes to a support group for friends and family of April Jones. 
On 31 March 2010, the Today Show ran a segment detailing the deaths of three separate adolescent girls and trolls' subsequent reactions to their deaths. Shortly after the suicide of high school student Alexis Pilkington, anonymous posters began performing organized psychological harassment across various message boards, referring to Pilkington as a "suicidal slut", and posting graphic images on her Facebook memorial page. The segment also included an exposé of a 2006 accident, in which an eighteen-year-old fatally crashed her father's car into a highway pylon; trolls emailed her grieving family the leaked pictures of her mutilated corpse. 
In 2007, the media was fooled by trollers into believing that students were consuming a drug called Jenkem, purportedly made of human waste. A user named Pickwick on TOTSE posted pictures implying that he was inhaling this drug. Major news corporations such as Fox News Channel reported the story and urged parents to warn their children about this drug. Pickwick's pictures of Jenkem were fake and the pictures did not actually feature human waste.
In August 2012, the subject of trolling was featured on the HBO television series The Newsroom . The character of Neal Sampat encounters harassing individuals online, particularly looking at 4chan, and he ends up choosing to post negative comments himself on an economics related forum. The attempt by the character to infiltrate trolls' inner circles attracted debate from media reviewers critiquing the series.  
The publication of the 2015 non-fiction book The Dark Net: Inside the Digital Underworld by Jamie Bartlett, a journalist and a representative of the British think tank Demos, attracted some attention for its depiction of misunderstood sections of the internet, describing interactions on encrypted sites such as those accessible with the software Tor. Detailing trolling-related groups and the harassment created by them, Bartlett advocated for greater awareness of them and monitoring of their activities. Professor Matthew Wisnioski wrote for The Washington Post that a "league of trolls, anarchists, perverts and drug dealers is at work building a digital world beyond the Silicon Valley offices where our era’s best and brightest have designed a Facebook-friendly" surface and agreed with Bartlett that the activities of trolls go back decades to the Usenet'flame wars' of the 1990s and even earlier. 
As reported on 8 April 1999, investors became victims of trolling via an online financial discussion regarding PairGain, a telephone equipment company based in California. Trolls operating in the stock's Yahoo Finance chat room posted a fabricated Bloomberg News article stating that an Israeli telecom company could potentially acquire PairGain. As a result, PairGain's stock jumped by 31%. However, the stock promptly crashed after the reports were identified as false.
So-called Gold Membership trolling originated in 2007 on 4chan boards, when users posted fake images claiming to offer upgraded 4chan account privileges; without a "Gold" account, one could not view certain content. This turned out to be a hoax designed to fool board members, especially newcomers. It was copied and became an Internet meme. In some cases, this type of troll has been used as a scam, most notably on Facebook, where fake Facebook Gold Account upgrade ads have proliferated in order to link users to dubious websites and other content. 
The case of Zeran v. America Online, Inc. resulted primarily from trolling. Six days after the Oklahoma City bombing, anonymous users posted advertisements for shirts celebrating the bombing on AOL message boards, claiming that the shirts could be obtained by contacting Mr. Kenneth Zeran. The posts listed Zeran's address and home phone number. Zeran was subsequently harassed.
Anti-Scientology protests by Anonymous, commonly known as Project Chanology, are sometimes labeled as "trolling" by media such as Wired ,  and the participants sometimes explicitly self-identify as "trolls".