Triplanar mapping
Texturing a surface without UV coordinates by projecting the texture along the three world axes and blending the projections by the surface normal.
A texture is normally applied through UV coordinates, but procedurally generated geometry — heightmaps, voxel terrain, cliffs sculpted in-engine — often has no good UVs, and whatever UVs exist stretch the texture across steep areas. Triplanar mapping skips UVs entirely and instead projects the same texture three times: once straight down and once from each side.
Each fragment decides how much of the three projections to show based on the surface normal — a vertical wall draws mostly from the side projections, flat ground mostly from the top — and the transition is a smooth blend. The cost is three texture fetches instead of one, plus extra work to get normal mapping right per axis. It is the standard choice for terrain and cheap enough to run on anything that lacks sensible seams.