Understeer is typical of front-drive cars and is the condition when you go into a turn and the front end of the car "pushes", or rather, when you turn the front wheels the car has a tendancy to go straight instead of turn. Usually results in you hitting the guardrail/wall/another car, etc., head-on.
Oversteer is more typical of rear-drive vehicles and is when you go into a turn and the rear end of the car tends to get "loose" and wants to slide out from under you. This usually ends up in a spin. Do it right and it could become a drifting manuever and you will be worshipped by those around you. [rolleyes]
Robert, it would be nice if you could maybe contribute something besides smartass comments every one in a while. If you didn't know well enough to answer him, then just say so.
Hey thanks for the help everyone. now i wont feel like such a *******. not only because i now know what overstear and understear but because i know that i am not afraid to ask stupid questions unlike some people.