A benefit trustee is a person appointed, or in some instances elected, to act as the trustee of an employee benefit trust.

The definition for trustee can be found at the following link:
http://definitions.uslegal.com/t/trustee/

An employee benefit trust is a trust created by funds provided by an employer for the benefit of its employees. Benefits may also be provided to dependents and other relatives of employees. Benefits provided by a benefits trust can be in the form of cash distributions such as bonus payments, loans, health and/or retirement benefits, or via ownership of shares in the employer company