Nolo's Plain-English Law Dictionary

Custodian

A term used by the Uniform Transfers to Minors Act (UTMA) and Uniform Gifts to Minors Act (UGMA) for the person named to manage property left or given to a child under the terms of either of those Acts. The custodian manages the property until the child reaches the age specified by state law -- 21, in most states. Then the child receives the property outright, and the custodian has no further role in its management.
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