What is the difference between flap load relief protection and overspeed protection?
Flap Load Relief – on the 757 and a few 767s, if the flaps are at 30 and Flaps 30 speed is exceeded, the flaps automatically retract to 25. On most 767s, if the flaps are at 25 or 30 and the placard airspeed is exceeded, the flaps automatically retract to 20. The flaps will automatically re-extend when airspeed is reduced. If the Flap Load Relief fails to operate when it should, the Trailing Edge light will illuminate and the FLAP LD RELIEF EICAS message will display
So flap load relief is a system that specifically protects the flaps. This is the result of accelerating to higher speeds.
Overspeed is a more general term and the actual speed that defines overspeed may vary with configuration, the 767/757 has a warning for that
Overspeed Warning – Master Warning, EICAS message, discrete light and siren when airspeed exceeds Vmo/Mmo.