The USS Enterprise, a Constitution-class starship, firing it's forward ventral dual phaser emitters.
A phaser emitter is a form of phaser weapon usually installed on Federation Starfleet spacecraft and space stations.
History and specifics[]
Phaser emitters can be installed either as single units in shuttlecraft, or in phaser turrets, banks of two, or arrays forming long strips in starships and stations. (TOS episode: "Arena", TNG episode: "The Outcast", DS9 reference: Star Trek: Deep Space Nine Technical Manual)