What is mast bumping, and is it the same as a power push over?

The rotor hub striking its teeter stops hard enough to damage the mast, a structural failure caused by excessive rotor flapping. It is not the same thing as a power push over: a power push over is an aerodynamic event, a nose-down pitch caused by unloading the rotor under thrust, while mast bumping is the structural consequence when flapping goes far enough to hit the stops. The two terms get conflated constantly, including on a teetering-rotor helicopter, where the word is used more often than on a gyroplane.