Long recoil
A locked-breech action in which barrel and breech stay locked together for the entire rearward stroke.
Rare, and mostly of historical interest. The barrel and the breech travel all the way back together — further than the length of the cartridge — before the breech is caught and held, and the barrel then returns forward on its own, extracting the case as it goes.
The Browning Auto-5 is the design almost everyone means by the term. It is why that shotgun’s receiver is squared off at the back, why the barrel visibly disappears into the gun when it fires, and why it needs a friction ring stack that the owner has to reset for light or heavy loads.