Mainstream jazz is a genre of jazz music that was first used in reference to the playing styles around the 1950s of musicians like Buck Clayton

Buck Clayton

Buck Clayton was an American jazz trumpet player who was a leading member of Count Basie’s "Old Testament" orchestra and a leader of mainstream-oriented jam session recordings in the 1950s. His principal influence was Louis Armstrong...

 among others; performers who once heralded from the era of big band

Big band

A big band is a type of musical ensemble associated with jazz and the Swing Era typically consisting of rhythm, brass, and woodwind instruments totaling approximately twelve to twenty-five musicians...

 swing music who did not abandon swing for bebop

Bebop

Bebop differed drastically from the straightforward compositions of the swing era, and was instead characterized by fast tempos, asymmetrical phrasing, intricate melodies, and rhythm sections that expanded on their role as tempo-keepers...

, instead performing the music in smaller ensembles

Musical ensemble

A musical ensemble is a group of people who perform instrumental or vocal music. In classical music, trios or quartets either blend the sounds of musical instrument families or group together instruments from the same instrument family, such as string ensembles or wind ensembles...

. The medium once lay dormant during the 1960s, but regained popularity in the 70s.