Foursquare is a location-based social networking service that allows users to check in at various venues using their mobile devices. Founded in 2009, it enables users to share their locations with friends and discover new places based on recommendations and reviews. The platform has evolved over the years, transitioning from a social check-in app to a tool for businesses. It now offers services like Foursquare City Guide, which helps users find popular spots, and Foursquare for Business, which provides analytics and marketing solutions for venue owners to engage with customers.