Indie rock is a sub-genre of alternative rock that originated in the United Kingdom and the United States in the 1980s. Indie rock is extremely diverse, with sub-genres that include lo-fi, post-rock, math rock, indie pop, dream pop, noise rock, space rock, sadcore, riot grrl and emo. Originally used to describe record labels, the term became associated with the music they produced and was initially used interchangeably with alternative rock. As grunge and punk revival bands in the US, and then Britpop bands in the UK, broke into the mainstream in the 1990s it became to be used to identify those acts that retained an outsider and underground perspective. In the 2000s, as a result of changes in the music industry and the growing importance of the internet, a number of indie rock acts began to enjoy commercial success, leading to questions about its meaningfulness as a term.