Light probe
A point placed in the scene that stores the incoming light from every direction, so moving objects can pick up the same baked illumination as the static geometry around them.
Without them a character running through a baked room looks flat and detached — all the baked lighting lives in the walls' textures, not on her. A probe samples the light at its position, usually compressed into spherical harmonics (nine coefficients per colour channel suffice for diffuse light), and the engine interpolates between the nearest probes.
Valve's Half-Life 2 (2004) popularised the trick with its "ambient cubes" for moving props. Today's engines scatter probe grids automatically or let artists place them by hand wherever the light shifts.