Open Street Map is a free map of the world created and updated by its users. It works similarly to Wikipedia in that contributors use GPS-devices to record geo-coordinates and upload the resulting data to Open Street Map.
BlindSquare uses the Open Street Map service to find information about streets, paths, highways, intersections etc. BlindSquare does not query Open Street Map for POI-data of venues like museums, restaurants, schools, libraries as this information is retrieved from Foursquare.