Root motion
Also said as In-place animation, Animation-driven movement, Foot sliding
Letting the animation decide how far the character moves. The animator moves the whole body in the clip, and the game follows it. Its opposite is in-place animation, where code moves the character and the clip marches on the spot.
Root motion plants the feet and gives moves real weight, but the controls then have to wait for the animation. In-place responds at once, but the feet slide if code and clip disagree on speed.
Say it
“Use root motion for heavy attacks and climbing, so the feet stay planted. Use in-place for the run, driven by code, and match the clip's stride to 5 m/s so that the feet do not slide.”
Where you’ve seen it
Both big engines treat it as a per-animation choice: Unreal's documentation says root bone movement does not affect the character until you enable Root Motion, and Unity has an Apply Root Motion setting.
Not to be confused with foot sliding
Foot sliding is the symptom: a planted foot skating across the floor. It appears whenever the speed in the code does not match the speed in the clip.