"Key-bedding," as a fault, arises when you mis-time the action intended to produce a tone, and mis-apply this force to the pads under the Keys instead of carefully timing its culmination and completion during key-descent and with the tone, and its cessation forthwith.
Source: wiktionary
"Keybedding" simply denotes the misapplication (or mistiming on to the pads under the keys) of the force intended to PRODUCE SOUND. In other words, the force (weight, or muscular work) is here applied too late during key-descent to be effective in producing the intended key-movement and tone. As a result, the tone-intended force is "buried" on the keybeds, instead of creating tone.
Source: wiktionary