Pop is a genre of popular music that originated in its modern form during the mid-1950s in the United States and the United Kingdom. During the 1950s and 1960s, pop music encompassed rock and roll. Rock and pop remained roughly synonymous until the late 1960s, after which pop became associated with music that was more commercial, ephemeral, and accessible. Pop music is so successful because the barrier for failure is so low. Pop is a wild mix of anything that is popular at any time given. In the 20s and 30s that was jazz and the more formulaic swing dance music. In the 40s country music, blues which became rock and roll in the 50s together and so on.
Pop music is different 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.