In orthopedic parlance, the "ankle joint" refers to the joint between the leg bones (tibia and fibula) and the uppermost bone in the foot, the talus. To form this joints, the lower ends of the tibia and fibula of the lower leg form an open mortise into which the uppermost rounded surface of the talus fits. This joint allows movement of the foot up (dorsiflexion) to about +20 degrees above horizontal, and downward movement of the foot (plantar flexion) to about -50 degrees below horizontal.
The second joint of the ankle is between the 2 largest bones of the foot, the talus and the calcaneus (heel bone), and is located below and slightly in front of the ankle joint. This is the subtalar joint which is responsible for inversion (the movement that allows you to walk on the side of your foot) and eversion (the opposite of inversion) movements. Under normal conditions, the subtalar joint allows about 30 degrees of inversion and 15 degrees of eversion.
The third joint, the transverse tarsal joint, is located between two sets of bones. The back side of the joint is composed of the talus and calcaneus bones, and the front side of the joint is composed of the navicular and cuboid bones, such that the surfaces of the talus and navicular bones are directly opposed to one another - the talonavicular joint component - and the surfaces of the calcaneus and cuboid bones make up the calcaneocuboid joint component. Because the talus and calcaneus bones have the subtalar joint between them, the anatomical relationships between the talonavicular joint component and the calcaneocuboid joint component of the transverse tarsal joint can change with movement of the subtalar joint. The direct effects of these changes are that when the talonavicular and calcaneocuboid components are approximately parallel (eversion position of the ankle), the transverse tarsal joint is flexible and allows adduction (toe-in) and abduction (toe-out) movements of the ankle as are needed during the heel strike phase of walking/running for shock absorbing. When these components are moved out of parallel (inversion), the transverse tarsal joint becomes rigid and, therefore, is able to transmit force as is needed during the toe-off (push-off) phase of walking/running.