What does all fours mean?
The definition of all fours
All` fours”
Etym: [formerly, All` four”.]

All four legs of a quadruped; or the two legs and two arms of a person. To be, go, or run, on all fours (Fig.), to be on the same footing; to correspond (with) exactly; to be alike in all the circumstances to be considered. “This example is on all fours with the other.” “No simile can go on all fours.” Macaulay.