The Formative period is a period of time in human history that is marked by the development of early civilizations and the emergence of cultural and social complexity. It is a period of transition from the Neolithic to the Bronze Age, and is characterized by the emergence of cities, the development of writing
From Wikipedia
Several chronologies in the archaeology of the Americas include a Formative Period or Formative stage etc. It is often sub-divided, for example into "Early", "Middle" and "Late" stages.