Metatile
A block of several tiles — often 2×2 or 4×4 — treated as a single unit for storage and level design, a memory trick from the 8-bit era.
The NES hardware drew 8×8 tiles, but describing a whole room in individual 8×8 tiles would have blown the memory budget. The answer was the metatile: a 16×16 block built from four hardware tiles, with the level then laid out in the larger blocks. Super Mario Bros stores its levels this way — a handful of metatile types covers all of World 1-1.
The idea lives on in modern tile editors as the "brush" or "stamp": you paint with a composite pattern rather than a single cell at a time. It is kin to the tileset (the palette of individual tiles) and autotiling, which picks the right edge tile for you.