Folding Pocket Knives feature some sort of a locking mechanism to prevent the blade from closing on itself when performing a cutting task.
Liner locks are the most common. A liner lock engages when the blade is pushed out. The lock snaps in place and engages the bottom of the blade to prevent it from closing on itself. To close the blade back, you have to manually push the liner out of the way for the blade to be able to close. It is one the strongest locking mechanisms for a pocket knife.
Frame lock is similar to a liner lock in the way it engages and disengages the blade. However, instead of a handle liner, the frame lock uses part of the frame itself to engage the tang and fix the blade.
Slip joint Traditional pocket knives utilize the slipjoint mechanism to secure the blade in place. However, it does not actually lock the blade and can close on itself if used for extreme cutting. When the blade is open, a tension from a spring or a flat bar is applied, holding the blade in place. The slipjoint pocket knives are ideal for light everyday tasks.
Lockback mechanisms are a basic design of locking a blade. This allows for heavier cutting tasks to be accomplished. A locking arm that sits along the spine of the handle features a hook that fits into a notch on the back of the blade. The hook uses tension from the back spring to lock the knife into place.
Midlock mechanism is the same as the lockback, but located in the middle of the handle. This was done because with heavier use, you may accidentally push the lockback trigger with the side of your hand, disengaging the mechanism and allowing the knife to close on itself. Benchmade and S.O.G. have come up with proprietary locking mechanisms that work in similar fashions. Benchmade has the AXIS lock and SOG has the Arc-Lock. When a blade is opened, a steel bar is pushed into position using springs, engaging the knife tang and locking the blade into place. The tang becomes wedged between the bar and a stop pin, preventing the blade from closing on itself during cutting tasks.