A locking latch mechanism that requires a rectangular hole in door edge for installation. Ubiquitous in pre-1940 homes, this type of lock is known by many other names.
(n.) A lock installed in a hollowed out or mortised cavity. Source: Dictionary.com Read more about Definition and Types of Locks
A square box--mortised into the door--that contains the mechanism (sometimes a variety of mechanisms) that opens, closes, and locks a door. Mortise locks are manufactured for interior and exterior doors.