What is Field Reeve?

Legal Definition
An officer elected, in England, by the owners of a regulated pasture to keep in order the fences, ditches, etc., on the land, to regulate the times during which animals are to be admitted to the pasture, and generally to maintain and manage the pasture subject to the instructions of the owners. (General Enclosure Act, 1845, § 118.) Sweet.
-- Black's Law Dictionary