Temporary performance. Frequently referring to a temporary position performing and carrying out the duties of an office without actually holding the position.
Law Dictionary – Alternative Legal Definition
A term employed to designate a locum tenens who is performing the duties of an office to which he does not himself claim title; e.g. “Acting Supervising Architect.” Fraser v. United States, 16 Ct. CI. 514. An acting executor is one who assumes to act as executor for a decedent, not being the executor legally appointed or the executor in fact. Morse v. Allen, 99 Mich. 303, 58 N. W. 327. An acting trustee is one who takes upon himself to perform some or all of the trusts mentioned in a will. Sharp v. Sharp, 2 Barn. & Aid. 415.