Fissure: A cleft or groove. A fissure can be normal or abnormal.

A fissure in the cerebral cortex is a normal feature. It is a deep fold that involves the entire thickness of the brain wall.

A fissure in the anus is distinctly abnormal. It is a painful crack in the edge of the anus and is very painful. Also called an anal fissure or fissure in ano.