Shooting an unloaded gun.
Practicing gun manipulations, including sight alignment and trigger press, with an empty firearm. Dry fire can be very beneficial, but it is also very dangerous. See Dry Fire Article.
Firing of an unloaded firearm to practice handling and shooting techniques. This can damage some types of actions, particularly rimfire unless a Dummy Cartridge, or Snap Cap is loaded to absorb the shock to the firing pin.