system of operation is that which uses the recoil
of the firearm
to function (that is, to lock/unlock the firearm's breech, to extract and eject the cartridge
case from the firearm, to feed a new cartridge into the chamber, and to ready the firing mechanism). In the short-recoil system, the breech-block remains locked to the barrel for a distance less than that of the length of the cartridge being fired. Somewhere before that distance, the barrel stops moving rearwards, and the breech-block is unlocked, to continue alone.
The means by which the breech-block may be locked are many - any method at all that provides a positive lock can be used. As examples: