Pop = popular, it's not a music style...
Like Joe Elliot (from Def Leppard) said:
"You know what, lets just make great songs,' and if they are all pop songs, they are still going to be guitar-based pop songs. Even the rolling stones had a top ten hit, its playing on guitars most of the time, it's just commercial. Pop is a strange word, pop's become this word that you think of as pap. 'Pop' is short for popular, and that can be anything from Black Sabbath to Charlotte Church."
http://www.rathole.com/crumbs/fireworks/10/leppard.asp
Or if Joe doesn't rock your boat, maybe Merriam-Webster dictionary will:
"POP:
Function: adjective
Etymology: by shortening
Date: 1880
1 : POPULAR <pop music>: as a : of or relating to popular music <pop singer> b : of or relating to the popular culture disseminated through the mass media <pop psychology> <pop grammarians> <pop society>
2 a : of or relating to pop art <pop painter> b : having, using, or imitating themes or techniques characteristic of pop art <pop movie>"
Ice