I just searched the UESP and there is no type of armor called "Caitiff Armor." I'm sorry, but it doesn't exist in the game as a separate armor type. I play on 360 with over 300 hours of game play and I have never seen/come across that type of armor. If you did see it on 360 it had to be a set of custom enchanted daedric.
edit - there is a rank of Dremora called Caitiff, but it isn't an armor type but a rank of Dremora. Here is the quote from the UESP:
[quote]Dremora Caitiffs are a low level rank of Dremora utilized by Mehrunes Dagon as berserkers and shock troops. They start appearing at player level 8 and are more powerful than Dremora Churls. These Dremora wear Dremora Caitiff Armor (50% chance they wear a helmet), Robes for Mages, which cannot be looted. Dremora Caitiff's are summoned by the spell Summon Dremora.[/quote]
So it does exist, but you can not access it or wear it. One more quote from the UESP:
[quote]All Dremora armor cannot be removed, and therefore can never be worn by the player. The exception are shields, which can be taken and used normally if they drop from a Dremora's hand when he dies[/quote]