Widely accepted and/or normalized. Lots of ideas currently in the mainstream weren't at one time. I mean, not that long ago, women and minorities in this country weren't allowed to vote. That hairstyle definitely isn't in the mainstream of fashion, yikes.

To be widely accepted and/or normalized. Lots of ideas that are currently in the mainstream weren't at one time. I mean, not that long ago, women and minorities in this country weren't allowed to vote. That hairstyle definitely isn't in the mainstream of fashion, yikes.

To become widely accepted and/or normalized. Lots of ideas that have gotten into the mainstream weren't accepted at one time. I mean, not that long ago, women and minorities in this country weren't allowed to vote. I hope that hairstyle never gets into the mainstream of fashion, yikes.

Well-established media outlets, such as newspapers and TV stations, that reach a mass audience, considered collectively. The term is especially used to contrast it with other forms of media that one considers more truthful and/or less biased. Often abbreviated as "MSM." It seems that people are becoming increasingly distrustful of the mainstream media.