Pop music is a genre of popular music that originated in its modern form in the United States and United Kingdom during the mid-1950s. The terms "popular music" and "pop music" are often used interchangeably, although the former describes all music that is popular and includes many different styles. "Pop" and " rock " were roughly synonymous terms until the late 1960s, when they became increasingly differentiated from each other.
Although much of the music that appears on record charts is seen as pop music, the genre is distinguished from chart music. Pop music is eclectic, and often borrows elements from other styles such as urban, dance, rock, Latin, and country ; nonetheless, there are core elements that define pop music. Identifying factors include generally short to medium-length songs written in a basic format (often the verse-chorus structure), as well as common use of repeated choruses, melodic tunes, and hooks.
Definitions and etymology
David Hatch and Stephen Millward define pop music as "a body of music which is distinguishable from popular, jazz, and folk musics". According to Pete Seeger, pop music is "professional music which draws upon both folk music and fine arts music".  Although pop music is seen as just the singles charts, it is not the sum of all chart music. The music charts contain songs from a variety of sources, including classical, jazz, rock, and novelty songs. Pop music, as a genre, is seen as existing and developing separately. Thus "pop music" may be used to describe a distinct genre, designed to appeal to all, often characterized as "instant singles-based music aimed at teenagers" in contrast to rock music as "album-based music for adults".
Pop music continuously evolves along with the term's definition. According to The New Grove Dictionary Of Music and Musicians , popular music is defined as "the music since industrialization in the 1800's that is most in line with the tastes and interests of the urban middle class."  The term "pop song" was first recorded as being used in 1926, in the sense of a piece of music "having popular appeal". Hatch and Millward indicate that many events in the history of recording in the 1920s can be seen as the birth of the modern pop music industry, including in country, blues and hillbilly music. 
According to the website of The New Grove Dictionary of Music and Musicians, called Grove Music Online , the term "pop music" "originated in Britain in the mid-1950s as a description for rock and roll and the new youth music styles that it influenced".  The Oxford Dictionary of Music states that while pop's "earlier meaning meant concerts appealing to a wide audience ... since the late 1950s, however, pop has had the special meaning of non-classical mus[ic], usually in the form of songs, performed by such artists as the Beatles, the Rolling Stones, ABBA, etc".  Grove Music Online also states that "... in the early 1960s, [the term] 'pop music' competed terminologically with beat music [in England], while in the USA its coverage overlapped (as it still does) with that of 'rock and roll'". 
From about 1967, the term was increasingly used in opposition to the term rock music, a division that gave generic significance to both terms. Whereas rock aspired to authenticity and an expansion of the possibilities of popular music, pop was more commercial, ephemeral and accessible. According to British musicologist Simon Frith, pop music is produced "as a matter of enterprise not art", is "designed to appeal to everyone" and "doesn't come from any particular place or mark off any particular taste". It is "not driven by any significant ambition except profit and commercial reward ... and, in musical terms, it is essentially conservative". It is, "provided from on high (by record companies, radio programmers, and concert promoters) rather than being made from below ... Pop is not a do-it-yourself music but is professionally produced and packaged".
According to Frith, characteristics of pop music include an aim of appealing to a general audience, rather than to a particular sub-culture or ideology, and an emphasis on craftsmanship rather than formal "artistic" qualities. Music scholar Timothy Warner said it typically has an emphasis on recording, production, and technology, rather than live performance; a tendency to reflect existing trends rather than progressive developments ; and aims to encourage dancing or uses dance-oriented rhythms.
The main medium of pop music is the song, often between two and a half and three and a half minutes in length, generally marked by a consistent and noticeable rhythmic element, a mainstream style and a simple traditional structure.  Common variants include the verse-chorus form and the thirty-two-bar form, with a focus on melodies and catchy hooks, and a chorus that contrasts melodically, rhythmically and harmonically with the verse.  The beat and the melodies tend to be simple, with limited harmonic accompaniment.  The lyrics of modern pop songs typically focus on simple themes – often love and romantic relationships – although there are notable exceptions.
Harmony and chord progressions in pop music are often "that of classical European tonality, only more simple-minded." Clichés include the barbershop quartet-style harmony (i.e. ii – V – I) and blues scale -influenced harmony. There was a lessening of the influence of traditional views of the circle of fifths between the mid-1950s and the late 1970s, including less predominance for the dominant function.
Development and influence
Throughout its development, pop music has absorbed influences from other genres of popular music. Early pop music drew on the sentimental ballad for its form, gained its use of vocal harmonies from gospel and soul music, instrumentation from jazz and rock music, orchestration from classical music, tempo from dance music, backing from electronic music, rhythmic elements from hip-hop music, and spoken passages from rap.
In the 1960s, the majority of mainstream pop music fell in two categories: guitar, drum and bass groups or singers backed by a traditional orchestra.  Since early in the decade, it was common for pop producers, songwriters, and engineers to freely experiment with musical form, orchestration, unnatural reverb, and other sound effects. Some of the best known examples are Phil Spector's Wall of Sound and Joe Meek's use of homemade electronic sound effects for acts like the Tornados. At the same time, pop music on radio and in both American and British film moved away from refined Tin Pan Alley to more eccentric songwriting and incorporated reverb-drenched rock guitar, symphonic strings, and horns played by groups of properly arranged and rehearsed studio musicians. 
During the mid-1960s, pop music made repeated forays into new sounds, styles, and techniques that inspired public discourse among its listeners. The word "progressive" was frequently used, and it was thought that every song and single was to be a "progression" from the last. Music critic Simon Reynolds writes that beginning with 1967, a divide would exist between "progressive" pop and "mass/chart" pop, a separation which was "also, broadly, one between boys and girls, middle-class and working-class." Before the progressive pop of the late 1960s, performers were typically unable to decide on the artistic content of their music. Assisted by the mid-1960s economic boom, record labels began investing in artists, giving them freedom to experiment, and offering them limited control over their content and marketing. This situation fell in disuse after the late 1970s and would not reemerge until the rise of Internet stars. Indie pop, which developed in the late 1970s, marked another departure from the glamour of contemporary pop music, with guitar bands formed on the then-novel premise that one could record and release their own music without having to procure a record contract from a major label.  In 2014, pop music worldwide was permeated by electronic dance music. 
A Scientific Reports study that examined over 464,000 recordings of popular music recorded between 1955 and 2010 found less variety in pitch progressions, growing average loudness levels,  less diverse instrumentation and recording techniques, and less timbral variety, which declined after reaching a peak in the 1960s.  Scientific American ' s John Matson reported that this "seems to support the popular anecdotal observation that pop music of yore was "better", or at least more varied, than today’s top-40 stuff." 
Technology and media
In the 1940s improved microphone design allowed a more intimate singing style and ten or twenty years later inexpensive and more durable 45 r.p.m. records for singles "revolutionized the manner in which pop has been disseminated" and helped to move pop music to 'a record/radio/film star system'. Another technological change was the widespread availability of television in the 1950s; with televised performances, "pop stars had to have a visual presence". In the 1960s, the introduction of inexpensive, portable transistor radios meant that First World teenagers could listen to music outside of the home. Multi-track recording (from the 1960s); and digital sampling (from the 1980s) have also been utilized as methods for the creation and elaboration of pop music. By the early 1980s, the promotion of pop music had been greatly affected by the rise of music television channels like MTV, which "favoured those artists such as Michael Jackson and Madonna who had a strong visual appeal".
Legitimacy in music criticism
The latter half of the 20th-century included a large-scale trend in American culture in which the boundaries between art and pop music were increasingly blurred.  Between 1950 and 1970, there was a debate of pop versus art.  Since then, certain music publications have embraced its legitimacy. According to Popmatters ' Robert Loss: "There’s a strong argument for the ' rockist' mode in music criticism—that it exists, and that it’s harmful—and poptimism has positioned itself as a corrective, an antidote. ... In general, the Old Guard of rock critics and journalists is depicted as a bunch of bricklayers for the foundations of the Rock and Roll Hall of Fame. True in part, which is to say, false. Like film studies, rock criticism of the late ‘60s and the ‘70s was an attempt to make popular music worthy of study; it was poptimism before its day." 
Pop music has been dominated by the American and (from the mid-1960s) British music industries, whose influence has made pop music something of an international monoculture, but most regions and countries have their own form of pop music, sometimes producing local versions of wider trends, and lending them local characteristics. Some of these trends (for example Europop) have had a significant impact of the development of the genre.
According to Grove Music Online , "Western-derived pop styles, whether coexisting with or marginalizing distinctively local genres, have spread throughout the world and have come to constitute stylistic common denominators in global commercial music cultures". Some non-Western countries, such as Japan, have developed a thriving pop music industry, most of which is devoted to Western-style pop. has for several years produced a greater quantity of music of everywhere except the USA. The spread of Western-style pop music has been interpreted variously as representing processes of Americanization, homogenization, modernization, creative appropriation, cultural imperialism, or a more general process of globalization.
In Korea, pop music's influence has led to the birth of boy bands and girl groups which have gained overseas renown through both their music and aesthetics.  Korean co-ed groups (mixed gender groups) have not been as successful.