One who derives existence and support from another.

Source: U.S. Courts

A person, other than the taxpayer or spouse, who entitles the taxpayer to claim a dependency exemption.

Source: Internal Revenue Service

A child who is under the care of someone else. Most children who are eligible to receive child support must be a dependent. The child ceases to be a dependent when they reach the "age of emancipation" as determined by State law, but depending on the State’s provisions, may remain eligible for child support for a period after they are emancipated.

Source: Office of Child Support Enforcement.