Your heel is the rear part of your foot. Most people walk by placing their weight first on one heel, then shifting to their toes before stepping with the opposite foot.
If you take tap dancing lessons, you'll learn to tap with both your toes and your heels — feet have heels, and so do shoes. The base of the palm of your hand is also a heel, and when you walk your dog on a leash, keeping her at your side, you're teaching her to heel. The word also describes the very end of a loaf of bread, or an utter jerk — this informal meaning comes from U.S. mobster slang.