Definition: The bony parts that you feel under you when you sit up straight on a firm surface.
They are part of the pelvic girdle and technically known as the Ischial Tuberosity.
Also Known As: Sits Bones, Sitz Bones, Ischial Tuberosity
Alternate Spellings: sits bones, sitz bones
Examples:
Many Pilates exercises, such as spine stretch and saw, begin with sitting up straight on the sit bones.

