I kno what they do but what does it stand for and do all planes have it? 
Thnaks for the help again! 
FMS = Flight Management System
Not all planes have them.... well... in a sense all planes do because the pilot is the ultimate FMS... but in the computerized sense, no. It's getting more and more common in GA aircraft, but it's still a high ticket $$$ item comparatively, and you can get close to all the features of a full FMS with something like the G-1000 cockpit.