I've often seen this used for humorous purposes, but I would assume it has a formal usage as well.
Mortos (read mooch) is a demon from the Spooky Realm.
As far as I can tell, it's basically used as an "aka" or "i.e." of sorts, but I didn't want to assume I knew how it worked, and start throwing around all the time while people shake their heads at me silently. I had no idea how to search for this, so I'm hoping somebody can tell me what this is called as well.