Detail texture
A high-frequency, tightly tiled texture blended in up close to hide the fact that the base texture goes blurry when the camera gets near.
A wall or ground surface carries a base texture of limited resolution. Stand right up against it and every texel is magnified until the surface turns to mush. The trick is to modulate in a second, usually grayscale texture tiled many times more densely — grit, pores, weave — so the eye sees crisp structure where there was only a smeared blob of colour. The detail texture fades out with distance so it does not interfere from afar.
The technique was common in late-1990s engines, among them Unreal (1998) and Tribes, back when texture memory was scarce. Higher base resolution, normal maps and virtual texturing have since taken over most of the job, but the idea survives in detail normal maps.