(n.) The relation which exists between three or more sets of points, a.a', b.b', c.c', so related to a point O on the line, that the product Oa.Oa' = Ob.Ob' = Oc.Oc' is constant. Sets of lines or surfaces possessing corresponding properties may be in involution.
Meaning of INVOLUTION in English
Webster's English dictionary. Английский словарь Webster. 2012