Mainstream is, generally, the common current of thought of the majority. However, the mainstream is far from cohesive; rather the concept is often considered a cultural construct. It is a term most often applied in the arts (i.e., music, literature, and performance). This includes:

something that is available to the general public;
something that has ties to corporate or commercial entities.

As such, the mainstream includes all popular culture, typically disseminated by mass media. The opposite of the mainstream are subcultures, countercultures, cult followings, and (in fiction) genre. Additionally, mainstream is sometimes a codeword used for an actual ethnocentric or hegemonic subculture point of view, especially when delivered in a culture war speech. It is often used as a pejorative term. In the United States, mainline churches are sometimes referred to synonymously as "mainstream."

整个google从某权威source解释的文章的结果都放在那了，断什么章了？除非是没完全读懂英文，那漏了(断章) 就是自己的问题了。