A PDF document (in French) summarizes both WMS and WMTS information.
WMS
The Web Map Service (WMS) is a mapping service that allows a user to dynamically view georeferenced maps and data by querying a server.
WMTS
The Web Map Tile Service (WMTS) is a mapping service that allows a user to dynamically view tiled georeferenced maps from a data server. Contrary to WMS, WMTS want to be faster and more efficient.
Flash
The new GeoclipAir application no longer requires Flash Player.