What does the word involution mean?

Usage examples for involution

  1. Two projective point- rows superposed on the same straight line are, however, not necessarily in involution, as a simple example will show. – An Elementary Course in Synthetic Projective Geometry by Lehmer, Derrick Norman
  2. We accept the law of evolution, but cannot conceive of evolution independent of involution and an Evolver. – The Eliminator; or, Skeleton Keys to Sacerdotal Secrets by Richard B. Westbrook