What term describes an unbalanced feed system in which the driven element of an antenna is fed both at the centre and a fraction of a wavelength to one side of centre?

A gamma match is an unbalanced matching system commonly used to feed a balanced driven element, such as the driven element of a Yagi antenna, using an unbalanced coaxial cable. The shield of the coax is connected directly to the center of the driven element, while the center conductor connects to a rod that attaches to the driven element a fraction of a wavelength out to one side. This single-sided connection visually resembles the uppercase Greek letter Gamma. It effectively matches the 50-ohm coax to the antenna's impedance while simultaneously acting as a balun, unlike a T match which requires a connection to both sides of the center.