The mainstream is the prevalent current thought that is widespread.

It includes all popular culture and media culture, typically disseminated by mass media. This word is sometimes used in a pejorative sense by subcultures who view ostensibly mainstream culture as not only exclusive but artistically and aesthetically inferior.

It is to be distinguished from subcultures and countercultures, and at the opposite extreme are cult followings and fringe theories.

In the United States, mainline churches are sometimes referred to synonymously as "mainstream."

 

Note:   The above text is excerpted from the Wikipedia article Mainstream, which has been released under the GNU Free Documentation License.