What is Foursquare Day?

If you've clicked around Twitter or Facebook today, you've probably seen a gazillion season's greetings for something called Foursquare Day, which is already being called history's first great social-media holiday. So what is Foursquare Day? Basically, the event is an homage to Foursquare, a location-based social networking service that lets users "check in" to various eating and drinking establishments.

On Foursquare, if you frequent a place enough, you can earn badges, or even become the "mayor" of the joint; you can also meet people in real life or just send them messages from the other corner of the restaurant. Meanwhile, the owners of the restaurant/bar/cafe are reaping a whole lot of free publicity. It's a win-win, and in recent months, Foursquare has gained a whole lot of popularity among social networking fans.

Foursquare Day is the logical evolution of Foursquare madness. The holiday was conceived by a Tampa Bay optometrist – and self-described social-media fiend – named Nate Bonilla-Warford. "Nate is amused by simple number relationships like squares and primes and he makes a big deal about Pi Day each year," reads copy posted to the official Foursquare Day page. "The thought struck him that since four-squared equals 16, it would be great to check into Foursquare on the 4th and 16th of the year, otherwise known as 4/16 or April 16th."

Get it? Good – we don't want to have to go through that again. Anyway, to judge by Web activity, there are a good deal of Foursquare Day parties planned for today, including an official Foursquare party here in New York City. For a while, the Foursquare Day team was operating a map with icons representing all the Foursquare Day parties. But earlier today, the icons were removed.

"Basically, Foursquare Day has been so overwhelmed with awesome responses from all over the world, that we simply couldn’t keep up," a Foresquare Day rep wrote on the official blog. "Sorry for the inconvenience, but we think this is awesome. The whole words loves #4sqday." Indeed.

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How will you celebrate? Let us know in the comments.