World of Warcraft Dupes fall under the category of WoW Exploits but they're so useful that they deserve their own page! It's fairly simple to explain what WoW Dupes do. They duplicate items. Sounds fairly harmless at first, but when people find a WoW Dupe Exploit they can end up getting endless supplies of the best equipment, and gold making them hugely rich ingame.
As with the WoW Exploits, if you find a WoW Dupe...do not tell anyone! Once again they're like gold, although generally duping has been dealt with by Blizzard, and very few people will release the methods of doing it (if there are any currently) as it's the type of information that will spread like wildfire.