Alternative refers to a variety of music from the 1980s to present. Initially designed as the alternative to mainstream music (hence the name), alternative heavily popularized in the 1990s. Due to this, many underground rock fands turned to Indie.
Alternative began in the eighties with bands like REM and U2 providing underground rock among the mainstream New Wave and Synthpop artists. The popularity of MTV skyrocketed the genre's popularity. Nirvana brought Grunge into popularity with their breakthrough album Nevermind.