Longman Dictionary of Contemporary English - shelf

~ n plural shelves 1 a long flat narrow board fixed onto a wall or in a frame or cupboard, used for putting things on or storing things on  (Put it back on the top shelf. | shelves of books | supermarket shelves) 2 a narrow surface of rock shaped like a shelf, especially underwater 3 off the shelf available to be bought immediately without having to be specially designed or ordered  (off-the-shelf computer software packages)  (- compare off­the­peg) 4 be (left) on the shelf a) old-fashioned considered to be too old to get married b) if a plan, idea etc is left on the shelf it is not used or considered  (- see also shelve)