The term is used to describe a process whereby adulthood is broken down into different phases, for example young adulthood, middle age, young elderly etc. (Brannen).
“In family systems theories, the ability of family members to distinguish or separate their identities, thoughts, and emotions from those of other family members.” Barker, 1999).

As defined by Brannen. The social work dictionary (4th ed.). Washington, DC: NASW Press.