The age of majority is the threshold of legal adulthood as recognized or declared in law. It is the moment when a person ceases to be considered a minor and assumes legal control over their person, actions, and decisions, thus terminating the control and legal responsibilities of their parents or guardian over them. Most countries set the age of majority at 18, but some jurisdictions have a higher age and others lower. The word majority here refers to having greater years and being of full age as opposed to minority, the state of being a minor. The law in a given jurisdiction may not actually use the term "age of majority". The term typically refers to a collection of laws bestowing the status of adulthood. Those under the age of majority are referred to as minors and are legally forbidden from enjoying certain privileges or rights. There are other exceptions, however, in which also those who have reached the age of majority can be referred to as minors. For example, if a country's age of majority is 18, but the legal drinking age is 21, then a 20 year old would still be considered a "minor" in situations involving buying or consuming alcohol. Another example is the age to consent to sexual activity, that in most of the cases in the world is under the age of majority, however, in other cases it can be even above the age of majority and even in that case the younger part, despite having already reached the legal adulthood, would be still referred to as minor or underage to consent to sexual activity.

An adult is a human or other animal that has reached full growth. The biological definition of the word means an animal reaching sexual maturity and thus capable of reproduction. In the human context, the term adult has meanings associated with social and legal concepts. In contrast to a non-adult or "minor", a legal adult is a person who has attained the age of majority and is therefore regarded as independent, self-sufficient, and responsible. They may also be regarded as a "major". The typical age of attaining legal adulthood is 18, although definition may vary by legal rights, country, and psychological development.