What is understeer?

Understeer happens when the front tyres are overloaded and can't corner as much as the amount you turn the steering wheel. Understeer can happen when entering a corner too fast. You'll be turning the wheel but the car will feel like it's pushing wide. It's the opposite of oversteer, and can be rectified by lifting off the accelerator or applying the brakes to slow down to a point where the car is no longer pushing wide.