1) Adolescence is defined as the period of transition between childhood and adulthood from ages 10-19. It is characterized by profound biological, intellectual, and psychosocial changes as individuals reach physical and sexual maturity.
2) General principles of adolescent development include gradual replacement of simple by complex structures/functions in a continuous, environmentally dependent process as adolescents transition from child to adult identities.
3) Growth and development during adolescence includes physical changes like puberty, cognitive advances from concrete to abstract thinking, and psychosocial challenges forming identities and relationships. Physical maturity is measured using Tanner staging.