Final answer:
Warping is the variation in thickness of a rotor, often caused by uneven heating and cooling, and can lead to braking issues.
Step-by-step explanation:
The term that refers to variations in thickness of the rotor is warping. Warping occurs when the rotor becomes uneven, typically due to excessive heat which causes different parts of the rotor to expand at different rates. This can lead to a variety of braking problems, including vibration or pulsation when the brakes are applied. Glazing refers to the rotor developing a shiny surface, while grooving and scoring are typically the result of the rotor being worn down by abrasive materials or damaged by contact with other components.