brake fade

noun, Automotive.

a gradual loss of braking power resulting from decreased friction between the lining and the drum or disc of the brake and usually caused by overheating.

Also called fade.

Examples from the web for brake fade

brake fade is a problem with drum brakes, but not so much with disk brakes.
brake fade can happen when the brakes are overheated from prolonged use or the brakes are out of alignment.
Continued overuse may increase brake fade until the vehicle cannot be slowed or stopped at all.
Second, after you figure out what type of brakes you have, you should know about brake fade.