Texture wrapping
The sampler rule for what happens when texture coordinates fall outside the 0–1 range.
UV coordinates address a texture from (0,0) to (1,1), but geometry routinely asks for 2.5 or −0.3 — a floor tiled across a large room, say. The wrap mode decides the answer: repeat tiles the image seamlessly, clamp-to-edge stretches the border pixel, mirror flips every other copy to hide seams, and border returns a fixed colour. It is set per axis, so a texture can repeat horizontally and clamp vertically. Repeat on a non-tiling texture produces the classic hard seam; clamp on a skybox smears the edges. The modes are fixed-function sampler state, unchanged in spirit since early OpenGL.