A wook/wookie is a term (sometimes used in a derogatory sense), that describes a class of people (almost exclusively male) in the jam-band/EDM festival scene that are tall, hairy, lacking hygiene, associated with drug use and have a tendency to borrow things. The origins of the word wook might precede decades earlier in The Grateful Dead scene but was not thoroughly defined until the early 2000s and has only come into wider mainstream use in the mid-2010s. 
It is important to make a distinction between wooks and the rest of the music festival scene that has evolved throughout the 2010s. There are many people who dress and look like wooks but do not hold many of the negative traits of being a wook. Often people would refer to themselves or friends as "wooks" in a non-serious manner.
Early Definitions in Urban Dictionary (mid-2000s)
Some of the earliest attempts to define wook/wookie online can be found on Urban Dictionary dating back to 2003-2005.  The most popular definition of wook (dated from May 27, 2005) states the following:
A wook meme
noun or adjective. a dirty, hairy, stinky, mal-nourished, dishonest creature that often travels in packs, with possibly and unfortunately, mangy, multi-colored dogson hand-made all natural, organic hemp leashes, or alone wandering aimlessly around a concert (usually "hippie music") parking lot with a few seemingly more important than the music goals; find as many mind altering substances and cram them into their bodies as fast and furiously as possible, get into the show somehow, don't lose the dog this time, and if by chance they come across unattended property such as a cooler, chair, backpack, or a beverage, it will then become their own.
also once inside the show and the music begins, even if it sucks, a true wook will never be able to tell the difference because once the substances take effect, many of them can actually be seen dancing and "gooving" to music that only they can hear. wooks are only useful in one way: if you are trying to warn or scare a younger more easily influenced friend about the dangers of drugs, just tell them to observe and study the behaviors of wooks in their natural surroundings, but warn them that if they get too close, they may risk becoming one themselves! 
Many these definitions try to differentiate wook/wookie from the term hippie and bohemian; the latter is used to describe a certain lifestyle while the former is used solely in a derogatory way. Another definition clears this by saying:
Wooks in a K-Hole
It is important to make the distinction between a hippie and a wook. Hippies can generally be viewed as positive, optimistic members of society with an idealistic goal for the betterment of society. Wooks are everything that you've been warned about in regard to hippies wrapped into a neat little package. 
Phish.net Forum Discussion (2010)
In a forum discussion on phish.net in 2010, users gave several definitions of wooks and generally agreed that it was a derogatory word. User johnnyd summed it up by adding "What really classifies a wook is their lack of preparedness for what should be normal situations, their expectation that they are what makes the scene happen even though they are just big moochers, general bad hygiene, air of superiority and tendency to one-up every story one might have." A small band of people disagreed with johnny d and thought wooks were fine characters, and that the people that he was trying to define were actually called "trolls." 
/r/festivals Subreddit (2014)
In 2014, a question was asked in /r/festivals asking what a wook was. The highest upvoted definition by the community stated that:
A wook and his cat
it's the guys that are outside every festival with a cardboard sign that has "need a miracle" written in body grime. will consume any drug passed their way with much gusto. tells you why they hate whatever band is playing and how anything they played after a certain show or date is garbage. incredibly loud. can be found lurking around meowing and bumming cigarettes. often times they will blatantly ask you for food or money. either shirtless or wrapped in a series of scarves and drug rug scraps. hygiene is more than questionable. a job? was raised in the festival scene. 
Later in the thread, there is a disagreement about the quality of the drugs that wooks sell to consumers. Some argue that they are "bunk" and that they are ripping you off while others say that they usually have "fire" and instead warns to be wary of college bros. 
Thump Article (2015)
David Garber published an article in April 2015 titled "How to Spot a Festival Wookie." In it, he gives a blueprint of what a wook is and touches upon past definitions that were agreed upon on Urban Dictionary , phish.net forum, and /r/festivals such as abuse of drugs, lack of cleanliness, and generally bringing bad vibes. Yet David adds new characteristics to the wook as the term has evolved to new developments in festival culture such as bragging about their pins and using Grassroots California hats stash pockets to hide their Ketamine . 
Bassnectar Tweet (2017)
On July 19th, 2017, Bassnectar tweeted "When 40 or 50 wooks come out of their K holes long enough to spew gibberish off their meaningless social media accounts it doesn't phase me."  Many thought that Bassnectar was going after his own fan base, in which a noticeable and loud portion of which consists of wooks.