The longest bone in the human body is the femur, commonly known as the thigh bone. The femur extends from the hip to the knee, providing structure, support, and enabling movement in the leg. It plays a critical role in bearing the body's weight during activities such as walking, running, and jumping. The femur is not only essential for mobility but is also a key site for muscle attachment, which aids in the strength and stability of the leg. Its length and strong composition make it a vital component of the skeletal system.