Foursquare is a location-based social networking website based on software for mobile devices. Essentially, it enables people to use mobile devices to interact with their environment. Users “check-in” at venues using a mobile website, text messaging or a device-specific application by running the application and selecting from a list of venues that the application locates nearby. Created in 2009 by Dennis Crowley and Naveen Selvadurai, the company reported in March it had 7 million registered users.

Per Bloomberg’s official post: “New York City is proud to be the home of both the powerhouse companies and small startups that are thinking big, creating new jobs, and leading the global economy. Foursquare is one such success story. That is why we are proud to join Foursquare?s founders and fans in celebrating the first global social media holiday. Today, April 16th?4/16, the fourth sixteenth of the year?is Foursquare Day in New York City and around the world.”

A range of activities and events will take place this Saturday for the check-in app’s users, including a tsunami fund raising relief effort in San Francisco, where a group will partner with Sapporo Beer, and a ?4sqDay food truck festival’ food drive, sponsored by a group of users in Las Vegas.