A graviton beam is a confined beam of gravitons.
A graviton beam could be emitted through a starship's deflector dish. This was implemented on board the USS Voyager in 2374 when Seven of Nine modified Voyager's navigational controls to allow the deflector to emit a resonant graviton beam that opened a portal to fluidic space. (VOY: "Scorpion, Part II") A heavy graviton beam was considered and rejected as a weapon against the Borg by the USS Enterprise-D in 2366. (TNG: "The Best of Both Worlds")