A music genre is a conventional category that identifies pieces of music as belonging to a shared tradition or set of conventions. It is to be distinguished from musical form and musical style, although in practice these terms are sometimes used interchangeably.
As a genre, pop music is extremely eclectic, often borrowing elements from other styles including urban, dance, rock, Latin and country; nonetheless, there are core elements which define pop.
Alternative rock (also called alternative music, alt-rock or simply alternative) is a genre of rock music that emerged from the independent music underground of the 1980s and became widely popular by the 1990s. Examples of this would be Seattle Grunge, Punk Rock, Post Grunge.