Texture filtering
How the GPU picks a colour when a pixel lands between texels — from blocky nearest-neighbour up to anisotropic sampling that keeps angled floors sharp.
A texel and a screen pixel almost never line up exactly, so the GPU has to guess. Nearest-neighbour grabs the closest texel and gives hard blocks; bilinear filtering weighs the nearest four; trilinear also blends between two mipmap levels and kills the visible seam where the levels switch. Anisotropic filtering takes extra samples along the direction the texture is squashed, rescuing floors and walls seen at a grazing angle.
Without filtering, distant textures shimmer and crawl as the camera moves — the same aliasing seen in all digital sampling, only on the surface.