Interphalangeal joints of the foot
The interphalangeal joints of the foot are the joints between the phalanx bones of the toes in the feet. Since the great toe only has two phalanx bones (proximal and distal phalanges), it only has one interphalangeal joint, which is often abbreviated as the "IP joint".
Source: Wikipedia — Interphalangeal joints of the foot (CC BY-SA 4.0)