Your femur is the large bone inside your thigh. The femur is the strongest bone in the human body.
In between your knee and hip joints is your femur, the only bone in the upper part of your leg. The femur isn't just strong, but is also the longest of your bones. Four-legged animals have femurs as well. When this word was originally used in English, it was an architectural term. In Latin, femur means "thigh" or "thighbone."