An interview with Spatial.ai about the collection and use of geo social data and its role within location intelligence. 
Geosocial data is simply location-based social media data. It is media content (mostly text) produced by people on social platforms that is tied to specific locations.
The location component is often coordinates in latitude and longitude, but it could be a tagged place or street address as well. This type of data is publicly available on nearly every major social platform including Twitter, Instagram, Flickr, event platforms, review sites, etc.