A ray gun is a type of directed energy weapon commonly found in science fiction references.
When Loomis saw T'Pol's phase pistol, during her and Jonathan Archer's visit to 2004 Detroit, he told her that she had a "nice ray gun" and didn't believe "that thing's for real" until she shot a hole in his car door. Later when he was arrested by the Detroit Police, he warned them that they had to find the lizard people, but to be careful because "they've got ray guns." (ENT: "Carpenter Street")
When Jean-Luc Picard remarked that Lily Sloane had set a phaser to kill, Lily remarked that it was her first ray gun. (Star Trek: First Contact)
When Tom Paris was debriefing Kathryn Janeway on the technology of The Adventures of Captain Proton, he told her to remember that it is a "ray gun, not phaser. Imagizer, not viewscreen. Earthlings, not Terrans." (VOY: "Bride of Chaotica!")