What does the word tap mean?

Usage examples for tap

  1. There was a light tap at the door. – General John Regan 1913 by George A. Birmingham
  2. Now when everybody's gone an' he's putting out the lights, you go an' tap at the door. – The Hole in the Wall by Arthur Morrison
  3. I gave a little tap at the door, but there was no reply. – The Shrieking Pit by Arthur J. Rees