A latch hook lock is a type of lock that uses a latch mechanism to secure a door or other closure. The latch consists of a bar with a hooked end that fits into a keeper or strike plate on the door frame when the door is closed. When the latch is engaged, the door is locked in place and cannot be opened without first releasing the latch.

The term "backset" refers to the distance from the edge of the door to the center of the latch mechanism. A latch hook lock with a 35mm backset would have a latch mechanism that is 35mm (about 1.4 inches) from the edge of the door. This measurement is important when selecting a latch hook lock, as it determines the size and placement of the keeper or strike plate on the door frame. It is also important to ensure that the backset of the lock is compatible with the size and configuration of the door and door frame.