A WFS (World Feature Service) allows a server to provide data streams for geographical entities of different types (polylines, points, polygons…), unlike the Web Map Service (WMS) that provides only the image for one or more layers. The data flows in a specific format, Geo Markup Language (GML). Access to the service is done by means of a formatted URL (Internet address).

See http://en.wikipedia.org/wiki/Web_Feature_Service