What is a mainstream site?

[porn-update]

For several days I see people in the forum to talk about mainstream site.

Maybe I'm an idiot, but I do not know what is a mainstream site.
But I also asked google, and he seems to be idiot as me, has not been able to give me a clear answer.

Someone can explain me the difference between mainstream site and adult site?

Thank you

[Chibbs]

porn site = tits.. pussy.. cock.. cum
mainstream = anything without tits..pussy..cock..cum

selling bibles? that's mainstream
selling clothes? that's mainstream
selling guides on how sigs are too big on forums = that's mainstream

[Focus]

Mainstream can be seen by a various audience, adults sites it is self-explanatory.

[j3rkules]

Sites that are appealing to the general public, as opposed to adult industry, being of interest only to a specific audience.