Pop music is a genre of popular music that originated in its modern form during the mid-1950s in the United States and the United Kingdom. The terms popular music and pop music are often used interchangeably, although the former describes all music that is popular and includes many disparate styles. During the 1950s and 1960s, pop music encompassed rock and roll and the youth-oriented styles it influenced. Rock and pop music remained roughly synonymous until the late 1960s, after which pop became associated with music that was more commercial, ephemeral, and accessible. Although much of the music that appears on record charts is considered to be pop music, the genre is distinguished from chart music. Identifying factors usually include repeated choruses and hooks, short to medium-length songs written in a basic format (often the verse–chorus structure), and rhythms or tempos that can be easily danced to. Much pop music also borrows elements from other styles such as rock, urban, dance, Latin, and country. Definitions and etymology David Hatch and Stephen Millward describe pop music as "a body of music which is distinguishable from popular, jazz, and folk music". According to Pete Seeger, pop music is "professional music which draws upon both folk music and fine arts music". David Boyle, a music researcher, states pop music as any type of music that a person has been exposed to by the mass media. Most individuals think that pop music is just the singles charts and not the sum of all chart music. The music charts contain songs from a variety of sources, including classical, jazz, rock, and novelty songs. As a genre, pop music is seen to exist and develop separately. Therefore, the term "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 music writer Bill Lamb, popular music is defined as "the music since industrialization in the 1800s that is most in line with the tastes and interests of the urban middle class." The term "pop song" was first 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