ARF-GEF
Sorry, no insult intended! It is as fgarc03 said, I was trying to nicely tease you.
I am not a locksmith, so to the many of you here who know more than I do, please feel free to chime in and correct anything that I misunderstand. I still have LOTS to learn! so here goes:
The mortise lock cylinders are round and threaded, with the intent of being screwed into a mortise assembly in a door. They are retained within the mortise in a similar way to a euro profile lock, with a screw that is run from the side and holds into a channel in the threads.
A rim cylinder is also round, but not usually threaded. In the back are two screw holes that are used to retain the rim cylinder within the lock assembly. They are (as I understand it) frequently used in panic bar locks, and some night-latch type locks.
Deadbolt locks are also frequently held in place with two screws from the back of the cylinder. The drive cam - usually a flat metal bar - passes through a slot or cross shaped cam that drives the bolt.
To add to the confusion, I have some cylinders that have both the threads of a mortise and the screw holes of a rim cylinder. Not sure what the correct term for those cylinders would be. Shall we make some up?

Morim? Mortrim? Rimortise? Rimtise?
Gordon
Just when you finally think you have learned it all, that is when you learn that you don't know anything yet.