What is the definition or description of: fissure?

Fissures are: Grooves or clefts in various anatomical structures such as the brain (transverse fissure between cerebrum & cerebellum), the skull (sphenoidal fissure), the liver (for the ligamentum teres), the lung (oblique fissure), the spinal cord (ventral median fissure), or other structures such as the palpebral fissure between upper & lower eyelids. Can also be a tear in a structure as an anal fissure.