Weaver's bottom
Inflammation of the bursa that separates the gluteus maximus muscle of the buttocks from the underlying bony prominence of the bone that we sit on, the ischial tuberosity.
Weaver's bottom is a form of bursitis that is usually caused by prolonged sitting on hard surfaces that press against the bones of the bottom or mid-buttocks.
In proper medical parlance, Weaver's bottom is called ischial bursitis