Definition of "all fours"

all fours

noun
1. The four legs of a quadruped.
2. The four limbs of a primate.
3. (card games) A card game similar to whist.
  Quotations
  'Twas a bad leg allowed me to read the Pilgrim's Progress, and Mark Clark learnt All-Fours in a whitlow.
  1874, Thomas Hardy, Far from the Madding Crowd
4. A certain game of dominos.