What does the word shelf mean?

Usage examples for shelf

  1. Probably Ken had found something interesting to keep him from noticing the alarm clock on a shelf in the laboratory. – The Year When Stardust Fell by Raymond F. Jones
  2. You are on the shelf. – Ted and the Telephone by Sara Ware Bassett
  3. Now go and get me that green book on the third shelf and I'll read to you for a while, if you want. – The Whirligig of Time by Wayland Wells Williams