Breech-lock

A breech-lock is a system for mounting camera lenses to camera bodies. The lens is attached to the camera by means of a rotating ring which is used to tighten the lens to the camera by friction. 
Other methods for mounting a lens to a camera include bayonet mount or thread mounts. 
A breech-lock can also be used to refer to the mechanism that locks closed the breech of breech-loading firearms and artillery. 