A tractor beam emitter was a starship component that projects a graviton beam called a "tractor beam". This graviton beam was capable of either attraction or repulsion.
The shuttlebays aboard Federation starships each have a tractor beam emitter mounted near the shuttlebay in order to guide shuttlecraft in. In addition, each shuttlebay has a tractor beam emitter mounted within. (TNG: "Time Squared")
The location of the tractor beam emitter on the secondary hull of the Enterprise-B
In 2293, the location of the tractor beam emitter, on the ventral side of the secondary hull, was labeled in the USS Enterprise-B master systems display on the ship's bridge. (Star Trek Generations)
In 2370, Ensign Taitt reconfigured the tractor beam emitters of the USS Enterprise-D in order to fire a particle beam at a sun to destroy a Borg ship with a solar fusion eruption. (TNG: "Descent, Part II")
In 2377, the USS Voyager's Emergency Command Hologram escaped from Quarren ships by firing on their tractor beam emitters. (VOY: "Workforce")