What is the meaning of involution?

noun

• Reduction in size of an organ or part (as in the return of the uterus to normal size after childbirth. )
• A long and intricate and complicated grammatical construction.
• Marked by elaborately complex detail.
  • synonyms: elaborateness, elaboration, intricacy
• The act of sharing in the activities of a group.
  • usage: "the teacher tried to increase his students' engagement in class activities"
  • synonyms: engagement, participation, involvement
• The process of raising a quantity to some assigned power.
  • synonyms: exponentiation
• The action of enfolding something.
  • synonyms: enfolding