means A flat horizontal surface, usually fixed to a wall or set inside a frame, on which objects are placed for storage or display.

from From Middle English shelfe, with roots in the Old English scylfe (a ledge or partition) and scylf (a crag or pinnacle). It's a cousin of words found across the old Germanic languages — Middle Low German schelf for a set of shelves, and related terms for splitting or cleaving — which fits the idea of a flat slab split off from something larger. The same family gave us the geographical 'shelf,' as in the continental shelf, where the land takes a level step before plunging into the deep.