Biologically, a child (plural: children) is generally a human between the stages of birth and puberty. Some vernacular definitions of a child include the fetus, as being an unborn child. The legal definition of "child" generally refers to a minor, otherwise known as a person younger than the age of majority. "Child" may also describe a relationship with a parent (such as sons and daughters of any age) or, metaphorically, an authority figure, or signify group membership in a clan, tribe, or religion; it can also signify being strongly affected by a specific time, place, or circumstance, as in "a child of nature" or "a child of the Sixties".

The United Nations Convention on the Rights of the Child defines a child as "a human being below the age of 18 years unless under the law applicable to the child, majority is attained earlier". Ratified by 192 of 194 member countries. Some English definitions of the word 'child' include the fetus and the unborn. Biologically, a child is anyone between birth and puberty or in the developmental stage of childhood, between infancy and adulthood. Children generally have fewer rights than adults and are classed as not able to make serious decisions, and legally must always be under the care of a responsible adult.