Which structure is a depression on the lateral pelvis where the femoral head fits snugly?

The acetabulum is the correct choice as it is the specific anatomical structure located on the lateral aspect of the pelvis. It serves as a socket that houses the head of the femur, forming the hip joint. This depression allows for a stable and secure fit of the femoral head, enabling a wide range of motion in the hip while maintaining joint integrity during weight-bearing activities.

The ilium is actually the uppermost and largest part of the hip bone, but it does not function as a socket for the femur. The sacroiliac joint is the joint between the sacrum and the ilium, which plays a crucial role in connecting the spine to the pelvis but is not involved in accommodating the femoral head. The femoral neck is the region just below the head of the femur and connects it to the shaft of the femur; however, it does not form a depression in the pelvis. The acetabulum's specific design is critical for the stability and functionality of the hip joint.