I don't have the slightest idea. I know what people think the Mainstream Media is — you know, the usual suspects: ABC, NBC, CBS, The New York Times — but the term isn't just outdated, it's antiquated.
Back in the 1960s, you could have made a plausible argument that American journalism was dominated by something called the Mainstream Media. I wouldn't have agreed with that assessment. Even then there were liberal and conservative and a whole bunch of middle-of-the-road news outlets.
But the networks and most especially The Times did exercise outsized influence. In 1969, Gay Talese came out with a book called "The Kingdom and the Power." No, it wasn't about the Roman, the British or the American empire. It was about a single newspaper, The New York Times. Talese wrote about it as if it were, by itself, a fourth branch — a near-equal partner —of the U.S. government.
The Times remains a great news-gathering organization, but such a book title today would be met with astonishment, if not outright derision.
We're not merely living in the middle of a changing media landscape. We inhabit a different media universe.
The first upheaval came with the growth of right-wing radio. According to Talkers.com, Rush Limbaugh alone boasts more than 13 million listeners, more than each of the network evening news shows, which attract between 7 and 9 million viewers.
Sean Hannity also reaches a bigger audience, with 12.5 million listeners, than the network news shows, and Glenn Beck and Mark Levin each claim around 7 million.
The top progressive talk radio host, Thom Hartmann, trails far behind, with 2 million listeners.
Doesn't the ratings supremacy of Mr. Limbaugh and the other conservative radio shows make them, by definition, part of the Mainstream Media?
Yet they continue to style themselves as principled outsiders bravely rebelling against a mythically monolithic Mainstream Media. Baloney. They're pure MSM.
Cable news ratings tell a similar story. For 2016, 14 of the top 15 cable news shows were on Fox, according to TVNewser.com. The top non-Fox cable news show was "The Rachel Maddow Show" on MSNBC, which clocked in at number 12.
Wikipedia defines "mainstream" as "current thought that is widespread."
Fox News's "current thought" isn't just "widespread," it's dominant.
But here's where we shift from a changing media landscape to an entirely new media universe.
To paraphrase Pogo, "We have met the media, and they are us."
In a revolution as profound as the invention of the printing press, a majority of Americans now belong to some segment of the media. Facebook has upwards of 200 million users in the United States, according to Statista.com, and nearly 2 billion around the world.
Many Facebook posts, to be sure, convey mundane information about family dogs and birthdays, but the social networking service has already become a major, if not thoroughly understood, player in the news business.
It's entirely possible — though by no means proven — that fake news stories spread on Facebook tipped the election to Donald Trump.
According to Buzzfeed, 17 of the top 20 false election stories either overtly supported Trump or attacked Hillary Clinton. And here's the amazing part. In the run-up to the election the top 20 false election stories generated 8.7 million "shares, reactions and comments on Facebook."
By comparison, the top 20 stories from 19 various real news sites generated only 7.4 million shares, reactions and comments.
That's right. False news stories generated more shares than real news.
Now we come to Mr. Trump's favorite medium, Twitter, which has around 57 million users in the U.S.
Mr. Trump used his huge Twitter presence — he has more than 25 million followers — to bludgeon 16 Republican opponents and to eke out an Electoral College victory over Ms. Clinton.
Moreover, his Tweets themselves are retweeted and further amplified by coverage from radio, network and cable news shows, plus Facebook.
That makes Mr. Trump the single most powerful voice in the rapidly expanding media universe.
In other words, Trump himself is the very face of the Mainstream Media.
So the next time you start complaining about "the media," remember that you're probably part of the media yourself. With enough Facebook friends, you might even be "mainstream."