An adult is a person who has attained the age of majority. The age of majority is the legally defined age at which a person is considered an adult, with all the attendant rights and responsibilities of adulthood. The age of majority is defined by state laws, which vary by state, but is 18 in most states.
Definitions of adulthood are often inconsistent and contradictory; a person may be biologically an adult, and have adult behavior but still be treated as a child if they are under the legal age of majority. Conversely, one may legally be an adult but possess none of the maturity and responsibility that may define an adult character.
Anyone who has not reached the age of adulthood is legally considered an infant. adult noun adultus, elder, fully developed person, fully grown person, grown-up person, mature person, one who has attained legal majority, person of age, person of voting age, pubes, senior Associated concepts: adult male, adult person, adult woman, age of majority.