43 C.F.R. § 3180.0-5
The following terms, as used in this part or in any unit agreement approved under the regulations in this part, shall have the meanings here indicated unless otherwise defined in such unit agreement:
Federal lease. A lease issued under the Act of February 25, 1920, as amended (30 U.S.C. 181 , et seq.); the Act of May 21, 1930 (30 U.S.C. 351-359 ); the Act of August 7, 1947 (30 U.S.C. 351 , et seq.); or the Act of November 16, 1981 (Pub. L. 97-98 , 95 Stat. 1070).
Participating area. That part of a unit area which is considered reasonably proven to be productive of unitized substances in paying quantities or which is necessary for unit operations and to which production is allocated in the manner prescribed in the unit agreement.
Unit area. The area described in an agreement as constituting the land logically subject to exploration and/or development under such agreement.
Unitized land. Those lands and formations within a unit area which are committed to an approved agreement or plan.
Unitized substances. Deposits of oil and gas contained in the unitized land which are recoverable in paying quantities by operation under and pursuant to an agreement.
Working interest. An interest held in unitized substances or in lands containing the same by virtue of a lease, operating agreement, fee title, or otherwise, under which, except as otherwise provided in the agreement, the owner of such interest is vested with the right to explore for, develop, and produce such substances. The rights delegated to the unit operator by the unit agreement are not regarded as a working interest.
43 C.F.R. §3180.0-5