Binocular depth cues are the 'things' that help us to judge distance. The two main ones that relate to binocular vision are:
1. Convergence.
This is the fact that as we get closer to an object, our eyes begin to point inward to remain focused on the object. I.e. we go cross eyed.
2. Disparity
This is the fact that our eyes both see a different image when focused on an object because they are actually looking at it from a different perspective (about 6 centimeters apart). This disparity changes based on the object distance from the observer so is also a cue used by our brain to judge distance.