A family of the Men of Bree. As was typical among the Men of that region, the name comes from a plant.
Harry Goatleaf at one time watched the West-gate of Bree, but threw in his lot with Bill Ferny and Saruman's thugs during the War of the Ring.
It is linked to honeysuckle or woodbine. Its French name, chèvrefeuille is also a medieval lay, and would therefore presumably have been familiar to Tolkien.