MSNBC? The MSM tag was in use (1992) before MSBNC ever existed (1996). It came about with the advent of the "alternative media" of Internet Blogs, initially due to the assertions of (often extremist) wacko Bloggers that their Web sites contained the "real truth" which the "mainstream media" refused to tell.
MSM are those media disseminated via the largest distribution channels, which therefore represent what the majority of media consumers are likely to encounter. The term also denotes those media generally reflective of the prevailing currents of thought, influence, or activity. Large news conglomerates, including newspapers and the broadcast media, which underwent successive mergers in the U.S. and elsewhere at an increasing rate beginning in the 1990s, are often referenced by the term. This concentration of media ownership has raised concerns of a progressive homogenization of viewpoints presented to news consumers. Consequently, the term mainstream media has been widely used in conversation (and the blogosphere), often in oppositional, pejorative, or dismissive senses, in discussion of the mass media and the media bias.
MSM are those media disseminated via the largest distribution channels, which therefore represent what the majority of media consumers are likely to encounter. The term also denotes those media generally reflective of the prevailing currents of thought, influence, or activity. Large news conglomerates, including newspapers and the broadcast media, which underwent successive mergers in the U.S. and elsewhere at an increasing rate beginning in the 1990s, are often referenced by the term. This concentration of media ownership has raised concerns of a progressive homogenization of viewpoints presented to news consumers. Consequently, the term mainstream media has been widely used in conversation (and the blogosphere), often in oppositional, pejorative, or dismissive senses, in discussion of the mass media and the media bias.