Surgical division of the Achilles tendon or one of the longest tendons in the body, (formally called the tendo achilles or the tendo calcaneus) is a tough sinew that attaches the calf muscle to the back of the heel bone (the calcaneus).

According to Greek mythology, Achilles's mother held him as a baby by the heel and dipped him in the River Styx to make him invulnerable, but the heel by which she held him remained unimmersed and hence vulnerable, as Paris' arrow in Achilles' heel later proved.

See Achilles' Heel, the Myth for more details.