The femur is one of the long bones in the human body, located in the upper leg. The femoral neck is a thin part of the femur that connects it to the pelvis and forms the hip joint with the acetabulum of the pelvic bone. The head of the femur refers to the rounded end of the bone that fits into the acetabulum, forming the ball-and-socket joint of the hip. This joint allows for a wide range of motion and is essential for many daily activities such as walking, running, and sitting.