Mainstream is a very common expression mainly used, both as an adjective and a noun, in its figurative sense to refer to:
- the prevalent attitudes, values, and practices of a society or group the common current thought of the majority.
According to Etymonline:
- also main-stream, main stream, "principal current of a river," 1660s, from main (adj.) + stream (n.); hence, "prevailing direction in opinion, popular taste, etc.," a figurative use first attested in Carlyle (1831). Mainstream media attested by 1980 in language of U.S. leftists critical of coverage of national affairs.
According to Ngram the expression became more and more popular since the mid 50's, probably with the diffusion of mass media. The term is currently often used in a good number of fields such as music, science, sociology, politics, education etc. to indicate the prevailing trend , but what was the initial context ( in the 50's) where this expression was first consistently used? Or was it just a common term that easily and quickly spread to all direction without a precise context?