2D lighting
Dynamic lights and shadows in a flat sprite world, faked with normal maps and 2D shadow casters because there is no real geometry to catch the light.
A 2D scene has no depth for light to fall across, so engines fake it. Per-sprite normal maps give each pixel a fictitious surface direction, letting a moving light produce highlights and self-shadowing as if the sprite had relief. Shadows are cast by treating sprite edges or collider shapes as occluders and projecting them away from each light.
The result — pioneered by games like Odin Sphere and spread by Unity's 2D Renderer and Godot's Light2D — gives pixel art a sense of volume without going 3D. It costs more than flat rendering and needs artists to author normal maps, which many pixel-art purists skip.