Cel shading
Rendering that imitates hand-drawn art by quantising light into hard bands and adding inked outlines.
Instead of smooth light falloff, cel shading (after "celluloid") thresholds the lighting into a few flat tones, so a surface looks painted rather than photographic. Outlines are added by finding edges in depth and normal data, or by drawing a slightly inflated black backside of the model. Jet Set Radio (Sega, 2000) was the breakthrough; The Legend of Zelda: The Wind Waker (2002) and Borderlands (2009) made the style popular.
The technique ages well precisely because it never tried to look real — a cartoon look dates far more slowly than the chase for photorealism.