Alternative in terms of music is defined as any type of music altering from the mainstream music, however there is a distinguishable style of music generally called Alternative rock (also alternative music, alt-rock or simply alternative; known primarily in the United Kingdom as indie). It is a genre of rock music that emerged in the 1980s and became widely popular in the 1990s. The term "alternative" was coined in the 1980s to describe punk rock-inspired bands on independent record labels that did not fit into the mainstream genres of the time. As a musical genre, alternative rock consists of various subgenres that have emerged from the independent music scene since the 1980s, such as grunge, Britpop, gothic rock, and indie pop. These genres are unified by their collective debt to the style and/or ethos of punk, which laid the groundwork for alternative music in the 1970s,

Though the genre is considered to be rock, some of its subgenres are influenced by folk music, reggae, electronic music and jazz among other genres. At times alternative rock has been used as a catch-all phrase for rock music from underground artists in the 1980s, all music descended from punk rock (including punk itself, New Wave, and post-punk), and, ironically, for rock music in general in the 1990s and 2000s.

While a few artists like R.E.M. and The Cure achieved commercial success and mainstream critical recognition, many alternative rock artists during the 1980s were cult acts that recorded on independent labels and received their exposure through college radio airplay and word-of-mouth. With the breakthrough of Nirvana and the popularity of the grunge and Britpop movements in the early 1990s, alternative rock entered the musical mainstream and many alternative bands became commercially successful.

Despite this explanation grabbed on wikipedia, there's a logical issue here: obviously music can't be same time pop and rock, and especially genres like british pop, who sell a lot of records because they're not alternative: nothing can be same time mainstream and alternative to mainstream itself, it's a clear contraddiction. It works only because mayority of listener adopted as trendy word, as they know nothing about real alternative bands. But the fact remain: alternative bands got few listeners, mainstream bands got many listeners, so it can't exist an alternative band selling dozen of millions of records.