Baked lighting
Lighting computed ahead of time in a tool and stored in textures or probes, so that runtime only looks up finished values instead of computing light every frame.
The idea is old: Quake (id Software, 1996) stored static lightmaps per surface and so got soft, precomputed shadows long before graphics cards could do anything of the sort in real time. Modern bakers run radiosity or path tracing offline and capture global illumination — light bouncing between walls — that would otherwise be too expensive.
The catch is that everything baked is frozen. Move a wall and the light no longer matches, and moving objects get no baked lighting at all unless they read separate light probes. That is why baked and dynamic light are nearly always combined in the same scene.