A person appointed by will or by law to assume responsibility for incompetent adults or minor children. If a parent dies, this will usually be the other parent. If both die, it probably will be a close relative.
Source: U.S. Courts
Person who fulfills some of the responsibilities of the legal parent role, although the courts or birth parents may continue to hold some jurisdiction of the child. Guardians do not have the same reciprocal rights of inheritance as birth or adoptive parents. Guardianship is subject to ongoing supervision by the court and ends at the child's majority or by order of the court.
Source: Children Welfare Information Gateway