A more thorough explanation:

cestui que use

An old-fashioned term for a person who benefits from assets held in a trust for the beneficiary's use. The term "beneficiary" is now used instead.

Archaic. The person for whose use and benefit property is being held by another, who holds the legal title to the property.

Example 1: John created a trust for the benefit of his daughter, Mary. Mary is the cestui que use of the trust.

Example 2: In the 18th century, cestui que use was a commonly used term in English law to refer to the beneficiary of a trust.

The term cestui que use is an old-fashioned term that was commonly used in English law to refer to the beneficiary of a trust. It refers to the person who benefits from assets held in a trust for their use and benefit. The term is now considered archaic, and the term "beneficiary" is used instead. The examples illustrate how the term was used in the past and how it is no longer commonly used today.