The term beneficial interest refers to the rights to an asset that are derived from the terms and conditions of an agreement. Beneficial interest oftentimes refers to the rights a party is deriving from a trust agreement.
When a donor directs assets to a trust, the trustee has a fiduciary responsibility to protect those assets. However, the trustee derives no beneficial interest from the trust. In this example, the beneficiary does not own the assets in the trust, but has a beneficial interest in those assets.
While a trust is the most commonly cited example of "beneficial interest," the term can be used whenever one party derives some sort of vested interest from an asset they do not own. For example, a person leasing a car enjoys the use of the automobile. They do not own the asset; however, they enjoy the benefits the agreement affords them.