Pukcab is a phrase used in place of the last name in your backup FaceBook account, as you cannot use the phrase "Backup" anywhere in your name on your FaceBook profiles, so it's the perfect way to get around FaceBook's strange laws, just so in case for whatever reason you loose access to your main account, or it gets blocked, suspended, banned, or deleted, you can have your other account ready to go, as long as you keep it as up to date with your main account. Just make sure you don't post what got your first account disabled on your Pukcab account.
Pukcab Accounts are more common for Roleplayers than regular FaceBook users.
FaceBook Roleplayer 2: "No, man! My account got deleted because of those sexy pictures I edited and posted up there."
FaceBook Roleplayer 1: "What about your FaceBook Pukcab account!?"
FaceBook Roleplayer 2: "Never made one! I lost everything!"