What's the deal with Festivus?

“Seinfeld” fans around the world gathered to air their grievances on Tuesday in celebration of Festivus, the holiday created by Frank Costanza on the popular 1990s sitcom, which has since become real annual tradition for thousands of people.

Kentucky Sen. Rand Paul was one of them.

“Christmas is a time for joy,” the Republican senator wrote on Twitter. “It is not a time to air grievances. That's what #Festivus is for.”

The alternative gathering calls for a metal pole instead of a tree, the airing of grievances (“You gather your family around and tell them all the ways they have disappointed you over the past year,” Frank Costanza explains) and the “feats of strength” — a father-son wrestling match that concludes the oddball holiday, dubbed a “Festivus for the rest of us.”

Like Frank Costanza, Paul has “a lot of problems with you people,” at least in Washington.

In honor of Festivus, here are 10 things you may not have known about the holiday and the “Seinfeld” episode that spawned it.

• The “Festivus episode,” which first aired on Dec. 18, 1997, was called “The Strike.” The plot revolved around Kramer’s decision to return to work at H&H Bagels, where he had been on strike for 12 years.

• Festivus is real. Daniel O’Keefe, a writer for the show, appropriated his family’s bizarre tradition for the episode. O’Keefe's father, Dan, invented Festivus in 1966.  “Actually, I didn’t want to put it on TV,” O’Keefe told CNN last year. “It was sort of a family disgrace, and then my younger brother let it slip that this went on, so the other writers and Jerry said, yeah, 'We’d like to give this to America.’ I said, I don’t think America wants it at all or should have it,’ but they prevailed upon me, and now the chickens have come home to roost.”

• Its acceptance surprised its inventor. In 2004, when the elder O’Keefe, a former Reader’s Digest editor, was informed by a New York Times writer that his holiday was catching on, he replied: “Have we accidentally invented a cult?”

• Maybe. Last year, a Florida man protesting a Nativity scene displayed inside the Florida Capitol building successfully applied to erect a 6-foot Festivus pole out of beer cans inside the statehouse rotunda. “What's the point? There is no point,” Chaz Stevens, who drove 450 miles from his Fort Lauderdale home to Tallahassee to put up the pole, told the Associated Press. “It’s ridiculous. This is the most ridiculous thing I could come up with.”

• It wasn’t always on Dec. 23. While Festivus is traditionally celebrated on Dec. 23, the O'Keefe family celebrated it anytime between October and May. And while most celebrate it on the Dec. 23, Festivus observers have been known to celebrate it on other days, hosting Festivus parties the weekend before Christmas.

• Festivus has gone mainstream. The holiday has become a worldwide celebration, with people from Australia to Indonesia gathering around their own metal poles — or at least tweeting about them.

• The pole was not part of O’Keefe’s original “holiday.” Another “Seinfeld” writer came up with the idea for the unadorned pole because, as George Constanza put it, "I find tinsel very distracting.” The real symbol of the holiday was a clock in a bag nailed to the wall in the O’Keefe home. “I don’t know why,” he said.

• The feats of strength weren’t part of the O’Keefe tradition, either. “I was not forced to wrestle my father,” O’Keefe said. “If I had, I would’ve been raised by the state of New York.”

• Another Festivus miracle! “Although it is not an official element of the holiday or its celebration," Mark Nelson notes on FestivusWeb.com, “the phenomenon of the Festivus Miracle is mentioned twice in the original episode. An obvious sendup to the phrase ‘Christmas Miracle,’ both manifestations of Seinfeld's ‘Festivus Miracle’ were caused by Kramer.”

• Seinfeld himself still gets a kick out of it.

Seinfeld gave fans another gift on Festivus — a rare standup set on "Late Night With Jimmy Fallon":