They are unique codes for one time use. U can use multiple codes with one credit card, but the codes themselves are one use each. Hope that clarifies :)
Actually what the mods are trying to find out is if the seller is issuing the reusable codes, that can be used again with a new credit card. Examples below:
Breakroom DVDONME DVDNIGHT MOVIENIGHT
Etc. So we can assume its none of these right? ^_^