The Achilles tendon is the strong, fibrous tissue located on the back of your lower leg. It connects the muscles of your calf to your heel bone, powering your movements whenever you walk, run, or leap.
Much like a superhero, the Achilles tendon has its own epic backstory. The term is named after Achilles, the Greek mythological hero who was nearly invincible thanks to being dipped in the magical River Styx by his mother. Unfortunately, his heel and a part of his tendon didn’t touch the water, leaving him physically vulnerable to attack. An injury to the Achilles' heel or tendon can significantly impair the ability to move around freely, so both terms are often used figuratively to point out a weak or unsafe position or situation.