Mainstream is, generally, the common current of thought of the majority. It is a term most often applied in the arts (for example, music, literature, and performance). This includes: something that's ordinary or usual; something that's familiar to the masses; something that's available to the general public. As such, the mainstream includes all popular culture, typically disseminated by mass media. The opposite of the mainstream are subcultures, countercultures, cult followings, underground… (More on Mainstream)