All of your weapons fall into one of three categories. These categories only matter for the sake of earning Badges (see Overdrives), and don’t really have an additional effect.
Automatic weapons refer to anything that will keep firing continuously when you hold the button down, until you either let go or the magazine’s empty. This obviously refers to “machine guns” like the High Fidelity or Fizzbot Rifle, but also refers to less obvious guns such as the Shocker or Murderang.
Single-Shot weapons inflict their damage through one big crowd-pleasing hit. This refers to both high-caliber hand cannons like the Dirty Harry or Ahab, as well as “grenade launchers” like the TNTeddy or Hair Spray Bomb.
Finally, Deployables linger in the environment on their own until consumed or their internal timers expire, and your involvement with them ends the moment they’re in play. Deployables include Turret Copters, Taunt Bots, and Proximity Mines.
An important note about Deployables is that there is no reason, once you have a few to play with, not to use them constantly. One of the keys to rapidly dealing with big enemies or huge waves of OD is to use as many different attacks at once as you can. Deploy Turret Copters to back yourself up, force enemies to wade through acid or Pulse Mines to get to you, and split their focus with Taunt Bots. Deployables are arguably the most potent weapons in the game, so use them as often as possible.