Oversteer is the opposite of
understeer. When you turn the
wheel, the car seems to turn too much -- it's too sensitive. One way to think about it is as follows: say you're driving a car around a bend, and you draw the
arc of the
curve. If your front wheels are not tangential to the arc, and indeed they are angled more outwardly than the tangent, then you have
oversteer. It means that if you turn a little bit, the car moves a great amount.
This is typically what happens when you skid or try to do donuts. If you go into the curve with too much speed (especially in front wheel drive vehicles), you tend to lose traction on the back wheels, while the front ones are still driving forward, so the back of the car fish-tails. The car is very sensitive or twitchy even to slight movements of the steering wheel.