Alternative rock is a genre of rock music that emerged in the 1980s and became widely popular in the 1990s. It typically refers to music that is outside of the mainstream and often encompasses a wide range of sub-genres such as indie rock, punk rock, and post-punk. Alternative rock often features unconventional song structures, experimental instrumentation, and politically or socially conscious lyrics. It is known for its diversity and for being less commercially oriented than other forms of rock music.