Pop/Rock is a genre of popular music which originated in the 1950s, deriving from rock and roll. The terms popular music and pop music are often used interchangeably, even though the former is a description of any form of music which is popular (and can include any genre), whilst the latter is a specific genre of music which has qualities which would make it appealing to a large audience. Pop music, as a genre, is very eclectic, often borrowing elements from other styles throughout its course such as urban, dance, rock, Latin and country, yet there are core elements which define it. Such include generally short-to-medium length songs, written in a basic format which is often the verse-chorus structure, which generally make usage of repeated choruses, have a melodic sound, and have catchy hooks. So-called "pure pop" music, such as power pop, features all these elements, and for instrumentation uses electric guitars, drums and a bass; in the case of such music, the main goal is usually that of being pleasurable to listen to, rather than having much artistic depth. Pop music is generally thought of as a genre which is commercially recorded and desires to appeal to a mass audience.