Light leaking
A rendering error where light appears where it should be blocked, typically when a wall is too thin for the method's resolution.
It shows up in most indirect and precomputed lighting methods. A light probe or a lightmap samples light at sparse points; put a thin wall between a lit and a dark side and interpolation can bleed light straight through it, so a dark room glows from the sun outside. Voxel-based GI and low-resolution shadow maps suffer the same way.
The opposite of shadow acne and peter panning, but related: all three are artefacts of sampling light and shadow too coarsely. Fixes are denser probes, geometry thicker than the probe spacing, or manually placed light blockers.