Tile attribute (attribute table)
The extra bytes that say which colour palette each background cell is drawn with — colour stored apart from shape to save memory.
The NES background was a grid of tiles (the nametable), but colour lived in a separate, far coarser table: 64 bytes giving one palette per 16×16-pixel area, four tiles at a time. Separating shape from colour saved memory but tied neighbouring tiles to the same hues. The ZX Spectrum took the idea furthest with one attribute byte per 8×8 cell, producing the infamous attribute clash. Planning where the palettes broke was an art in itself — pixel artists deliberately placed detail along the attribute boundaries.