Intergluteal cleft

The intergluteal cleft is the groove between the buttocks that runs from just below the sacrum to the perineum, containing the anus. Colloquially, the intergluteal cleft is known as bum crack or butt crack. The name "intergluteal cleft" is used because it forms the visible border between the external rounded protrusions of the gluteus maximus muscles.
There are several disorders that can affect the intergluteal cleft including inverse psoriasis, caudal regression syndrome, and pilonidal disease.