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Lightmap

A lightmap is a data structure used in lightmapping, a form of surface caching in which the brightness of surfaces in a virtual scene is pre-calculated and stored in texture maps for later use. Lightmaps are most commonly applied to static objects in realtime 3d graphics applications, such as video games, in order to provide lighting effects such as global illumination at a relatively low computational cost.

Wiktionary

lightmap

n. (context computer graphics English) A precomputed data structure that stores the brightnesses of surfaces in a video game, etc.