the number 4:
She is married with four children.
They arrived just after four (=four o'clock).
Luke will soon be four (=four years old).
supporting your body with your hands and knees:
He was down on all fours playing with the puppy.
a hit in cricket that scores four runs because it goes over the edge of the playing area
a team of four people who row a racing boat, or the boat that they row
places or countries that are very far away from each other:
People from the four corners of the world have come to Ontario to make it their home.