Ischial bursitis
Bursitis: 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.
Ischial bursitis 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.
Ischial bursitis is also referred to as weaver's bottom because weavers traditionally would weave in a position that aggravated the affected bursa.