Hillary Clinton just introduced America to a new villain in the 2016 election cycle. It's not the Koch brothers, or Russia, or the "vast right-wing conspiracy," the term she coined in back in 1998. In fact, it's a fringe right-wing conspiracy, an online movement known as the "Alt-right."

"The de facto merger between Breitbart and the Trump campaign represents a landmark achievement for the 'Alt-right,'" Clinton said at a Thursday rally in Reno, Nevada. "A fringe element has just taken over the Republican Party."

More than a couple people in the audience and at home might be wondering exactly what Clinton is talking about.

The "Alt right," as it's come to be called, has been diagnosed as a new strain of hardcore anti-liberal politics that Donald Trump has cultivated, and relied on, throughout his presidential run. Now that Clinton has decided to use the term, it's likely to get more mainstream coverage.

One easy way to approach a definition is by clearing up what the "alt-right" is not: they are not just Tea Party people, or NRA people, or Islamophobes, though they may participate in those circles, too.

Practically speaking, it's a subculture of online tough guys and keyboard warriors that arose out of message boards and social media. They read, and contribute to, outlets like Breitbart News and InfoWars. Some of its tech-savvy adherents recently got attention by developing ways to identify Jews by their surnames online. It's a community and ideology formed on the internet, through anti-government conspiracy theories and harassing liberals, women and people of color.

Beyond its pet issues and principles, like most "-isms," the term is best understood by looking at its adherents.

You have put-on provocateurs like Breitbart "tech editor" Milo Yiannopoulos, who coasted to mini-stardom online by preaching against P.C. culture, deflecting all criticism with his identity as an openly gay man who dresses like Macklemore. You have über-libertarian and Sandy Hook and 9/11 Truther Alex Jones, who runs the Sovereign-Citizen-style news network InfoWars.com, which warns viewers about government-regulated water turning frogs gay.

You have Roger Stone, onetime Nixon dirty trickster who has been a close adviser to Trump this election, feeding the alt-right audience with narratives about Clinton's fictional brain spasms and rigged Democrat electioneering. And of course, you have Milo's boss, Steve Bannon, who took over the direction of Breitbart News as executive chairman after its founder and namesake died in 2012, and is now CEO of the Trump campaign itself.

Breitbart News, indeed, is fingered by most people as "Alt-right" HQ: Ex-Breitbarters who walked out earlier this year over the site's wholesale embrace of Trump like to argue that Andrew Breitbart himself would be disgusted at what his baby has become.

"I am absolutely appalled by what Breitbart's become," said onetime editor-at-large Ben Shapiro. "I think Bannon has perverted Breitbart's legacy."

But the site has always been obsessed with "P.C. culture," hatred of protesters, fear of immigrants, and the white man's burden of reverse-racism. Shapiro himself would rail against Palestinians, black people, rap music and liberal politicians week by week. How Breitbart News has changed since its founder's death is never really addressed by the expats.

At any rate, Bannon, and Breitbart's legacy, now work for Trump.

Exactly why Clinton wanted to introduce this term into the mainstream is unclear: it certainly fits into her strategy of painting Trump as vulgar threat ("Dangerous Donald") that rational people, Republican or Democrat, need to see crushed.

But lecturing audiences on a relatively obscure internet subculture is an odd way to connect with most Americans, particularly the older disgruntled whites that Clinton wants to peel off Trump.