The term pop has been used since the early twentieth century to refer to popular music in general, but from the mid-1950s it began to be used for a distinct genre, aimed at a youth market, often characterized as a softer alternative to rock and roll.[6][7] In the aftermath of the British Invasion, from about 1967, it was increasingly used in opposition to the term rock music, to describe a form that was more commercial, ephemeral and accessible.[8]