A fistula is an abnormal passage or communication, usually between two internal organs or leading from an internal organ to the surface of the body.

It is frequently designated according to the organs or parts with which it communicates; such as, anovaginal, brochocutaneous, hepatopleural, pulmonoperitoneal, rectovaginal, urethrovaginal, etc.

Such passages are frequently created experimentally for the purpose of obtaining body secretions for physiologic study.