Classic rock was originally conceived as a radio station programming format which evolved from the album oriented rock (AOR) format in the early-1980s. In the United States, this rock music format now features a large and nearly unlimited playlist of songs ranging from the early-1960s through the early-1980s with more emphasis on the earlier hits by artists associated with the loosely-defined "classic rock radio era".
In common speech, the term also refers to earlier rock bands, often seen as more talented or original than later acts - this definition can be ended at a subjective date, most often between 1975, when rock became more commercialized as arena rock took hold of the scene, the early 1980s, when the blues influence faded away, or 1991, when Nirvana and grunge replaced the hair metal bands.
On some occasions, two eras of classic rock radio are indicated. XM provides a station for "Early Classic Rock" from the sixties-seventies and one for "Late Classic Rock" from the seventies-eighties.
Additionally, a "Deep Classic Rock" station is sometimes offered for lesser classic rock radio hits.