What term is used to describe a person under the age of 21 who is missing and not declared emancipated?

The correct term to describe a person under the age of 21 who is missing and not declared emancipated is "Juvenile." In legal contexts, a juvenile is typically defined as an individual who has not yet reached the age of majority, which is often 18 years old in many jurisdictions. Since the question specifies that this individual is under 21 and not emancipated, they remain under the protection and authority of their parents or guardians, classifying them as a juvenile.

Understanding this term is crucial for law enforcement and professionals dealing with missing persons cases, as it helps in determining the appropriate procedures and legal frameworks that apply to individuals who are minors. The other options do not accurately represent the legal status or definition pertinent to individuals who are under the age of 21 and missing.