All fours means being on your hands and knees. When you're on all fours, you're down low with your palms and knees touching the floor, like how a baby crawls before learning to walk.

You might drop to all fours to search for a lost earring under the couch, or to get a closer look at an interesting bug on the ground. Dogs and cats naturally move around on all fours, which is why we call them four-legged animals or quadrupeds.

The phrase comes from the simple fact that you're using all four of your limbs to support yourself. Athletes sometimes start races from all fours in a sprinter's crouch. Rock climbers navigating a narrow ledge might get down on all fours for better balance and safety.

You'll also hear the phrase in the expression “down on all fours,” which emphasizes the position: “She got down on all fours to look under the bed.” It's a practical position when you need stability, want to stay low, or need to use your hands to feel around in a tight space.