A flat, usually rectangular structure composed of a rigid material, such as wood, glass, or metal, fixed at right angles to a wall or other vertical surface and used to hold or store objects. The contents or capacity of such a structure. Something, such as a projecting ledge of rock or a balcony, that resembles such a structure. A reef, sandbar, or shoal. Bedrock. off the shelf From ready-made merchandise in stock: supplies that were available off the shelf. on the shelf In a state of disuse. on the shelf Unemployed. on the shelf Out of circulation. on the shelf Retired.