An Involution

1. Entanglement; a spiralling inwards; intricacy.
2. A complicated grammaticalconstruction.
3. (mathematics) An endofunction whose square is equal to the identity function; a function equal to its inverse.Hyponyms: complex conjugation, complementation
4. (medicine) The shrinking of an organ(such as the uterus) to a former size.
5. (physiology) The regressive changes in the body occurring with old age.
6. (mathematics, obsolete) A power: the result of raising one number to the power of another. Involution (mathematics) - Wikipedia

Involution - Wikipedia