means a narrow horizontal shelf or projection, especially one jutting from a cliff, wall, or other vertical surface.

from From Middle English 'legge,' likely related to the verb 'lay' — the idea of something laid out flat or set in place, as a beam or ledge laid horizontally. The sense of a rock shelf or stony projection emerged later. A cousin, then, of 'lay' and 'ledger' (a book that lies flat), all rooted in the old notion of putting something down on a level surface.