What is a mortis lock?

I have be told to look out for a mortis lock tomorow when looking at student housing but am not sure what it is.

Answers: this is a mortise lock

You know what a Yale key looks resembling, well a mortice knob is the other kind, where on earth the key have a series of oblong teeth which open the lock.
The bit of the lock that go in and out of the door frame is rectangular fairly than wedge shaped. It's much harder to break into.