(anatomy, zootomy) A gluteal muscle which arises from the front of the sacrum and the ischium or sacrotuberous ligament, passes out of the pelvis through the greater sciatic foramen, and inserts into the greater trochanter of the femur, serving in humans to rotate the thigh laterally.

A neuromuscular disorder that occurs when the sciatic nerve is compressed or otherwise irritated by the piriformis muscle, causing pain or numbness in the buttocks and legs.