Hip joint, knee joint, ankle joint, elbow joint.

Answer

### Step-by-Step Text Solution:

1. **Hip Joint**:
- The hip joint is classified as a ball-and-socket synovial joint.
- It is formed by the articulation between the pelvic girdle (specifically the pelvic acetabulum) and the head of the femur.
- This structure allows for a wide range of motion in multiple directions.

2. **Knee Joint**:
- The knee joint is also known as the tibiofemoral joint.
- It is a synovial joint formed between three bones: the femur, tibia, and patella.
- This joint primarily allows for flexion and extension of the leg.

3. **Ankle Joint**:
- The ankle joint is referred to as the talocrural joint.
- It is a synovial joint located in the lower limb and is formed by the tibia and fibula (the bones of the leg) and the talus (a bone in the foot).
- Functionally, it is classified as a hinge joint, allowing for dorsiflexion and plantarflexion.

4. **Elbow Joint**:
- The elbow joint is a complex hinge joint.
- It is formed between the distal end of the humerus (in the upper arm) and the proximal ends of the ulna and radius (in the forearm).
- This joint primarily allows for flexion and extension of the forearm.