Looks like it's registered users, as of a year ago.[0] [0] http://www.businessinsider.com/foursquare-surpasses-45-million-registered-users-and-begins-collectin

Looks like it's registered users, as of a year ago.[0] [0] http://www.businessinsider.com/foursquare-surpasses-45-million-registered-users-and-begins-collecting-data-in-new-ways-2-2014-1 http://www.businessinsider.com/foursquare-surpasses-45-milli...