Transition

n.
  1. Passage from one place or state to another; charge; as, the transition of the weather from hot to cold.
  2. (Mus.) A direct or indirect passing from one key to another; a modulation.
  3. (Rhet.) A passing from one subject to another.
  4. (Biol.) Change from one form to another.
    5. Transition rocks (Geol.),
    a term formerly applied to the lowest uncrystalline stratified rocks (graywacke) supposed to contain no fossils, and so called because thought to have been formed when the earth was passing from an uninhabitable to a habitable state.