Real Dictionary

understeer in American English
the tendency of a motor vehicle, esp. a race car, to have its front tires slide outward on a turn
intransitive verb: to undergo understeer, esp. excessively
noun: a handling characteristic of an automotive vehicle that causes it to turn less sharply than the driver intends because the front wheels slide to the outside of the turn before the rear wheels lose traction

understeer in Automotive Engineering
noun: Understeer is the tendency of a vehicle to turn less sharply than expected.

understeer in British English
(of a vehicle) to turn less sharply, for a particular movement of the steering wheel, than anticipated