shelf

shelf /ˈʃɛlf/ noun
plural shelves /ˈʃɛlvz/
shelf
/ˈʃɛlf/
noun
plural shelves /ˈʃɛlvz/
Britannica Dictionary definition of SHELF
[count]
1 
: a flat board which is attached to a wall, frame, etc., and on which objects can be placed
— see also bookshelf
2 
geology : a flat area of rock, sand, etc., especially underwater — see also continental shelf

off the shelf

: directly from a store without having to be specially made or ordered

on the shelf

: in an inactive state : not active or being used