A short recoil operation firearm is an autoloading semiautomatic or automatic firearm whose barrel and bolt move rearward together in the first part of the weapon's cycle. After a short distance, the barrel and the bolt separate, with the barrel stopping and the bolt continuing to move backwards to both compress the recoil spring or equivalent mechanism and also to permit the extraction of the casing from the chamber. The casing may move out of the chamber on its own, but generally is removed by an extractor either attached to the bolt or externally, generally to the slide.
The primary reason the barrel moves slightly is to permit the operation of an unlocking mechanism, which unlocks the barrel from the bolt. This locked breech is more suitable for higher pressure ammunition, and the fact that the initial component of the recoil occurs with the bolt still locked to the barrel means that by the time the chamber opens most of the ejecta is already gone or at rest in the barrel, making the operation cleaner.
John Moses Browning is famous for using the short recoil method on most if not all of his autoloading firearms. The Colt 1911 and its ilk, as well as the Browning Hi-Power, his two most famous pistol designs, both use a short recoil system with a tilting barrel. In the 1911, the barrel lugs pull the rear of the barrel downwards as it recoils, which unlocks it from the bolt; the barrel stops short, still slightly elevated, until the slide returns to battery and moves it back into position. The Hi-Power is similar, but rather than lugs on the barrel, there is a bar attached to the frame crosswise which engages a slot in the barrel as it recoils to pull it downwards. This is why slow motion and still images of these guns firing show the barrel pointed slightly upwards during cycling.
There are other methods of locking which are also short recoil, however. The toggle bolt, originally used in the first fully automatic machine gun the Maxim gun can be used in a short recoil system (although it can also be used in a delayed blowback system such as the Pedersen rifle). This method went on to be used in the famous German Mauser C96 and Luger pistols, distinctive for the toggle which flips up from the top of the gun during operation. Some guns, like the Beretta Px4 Storm, have rotating barrels. As the barrel and bolt recoil, cams on the barrel along with torque generated by the rifling spin it to disengage locking lugs, and the bolt is freed to continue rearward while the barrel halts.