Foursquare Day is celebrated on April 16, marking the anniversary of the geolocation app, Foursquare. The date is derived from the mathematical expression 4×4=16, which corresponds to April 16. This holiday is observed in over 100 cities worldwide, where enthusiasts engage in various activities such as check-ins, parties, and lectures to celebrate the app's functionality in sharing locations. The day originated in Tampa, Florida, when Nathan Bonilla-Warford proposed the idea, which gained traction through community support and social media promotion. Initially, the app experienced significant user engagement, with hundreds of thousands of check-ins and new sign-ups during its first celebration. Foursquare provides promotional items like stickers and shirts to encourage participation, while allowing community members to organize events according to their preferences.