A mortice lock is a traditional lock which you will find on older buildings. This is because they were widely used before the invention of euro cylinder locks. Many people refer to these as Yale locks as Yale were one of the original companies to manufacture them. Originally these locks only used a mortice shaped cut out but modern re-designs now incorporate a euro fitting inside the traditional mortice lock case design.
Mortice locks and latches come in a variety of forms. Technically speaking a mortice door lock is operated by a long old style mortice key. This shape is what most people would image a key hole to look like. In modern days the key hole shape has changed to euro (light bulb shape) and oval. As well as the locking type there are also different options you can have in terms of locking style such as deadlocks, sashlocks and bathroom locks.
Replacing a mortice deadlock is a relatively simple job once you have measured up for your requirements. The most common backsets in deadlocks are 2.5" and 3". They are usually brass or chrome finish on the faceplate and the last choice you will have to make are wether you want the lock to incorporate a handle (sashlock) or just deadlock only with the key.
Mortice deadlocks are only use on wooden doors. The type of lock in use depends on your requirements. If you want to be to open the door with a handle then you will need a sashlock. If you want key only operation the it is deadlock you are after. There is also the option to not use a lock and operate the door on the tubular latch only.