Warforged
Warforged items are upgrades of non-Tier 16, Tier 17 and Tier 18 items that have a slim chance to apply to drops from Normal, Heroic and Mythic mode boss encounters in Siege of Orgrimmar, Highmaul, Blackrock Foundry and Hellfire Citadel. It also applies to items dropped from the world bosses Ordos, Drov the Ruiner, Tarlna the Ageless, Rukhmar and Supreme Lord Kazzak. The Warforged designation awards an additional six item levels to an item.
While drop rates for Warforged items are rare, they are slightly more common in larger raid groups. Additionally, using a 
[Warforged Seal] (for Siege of Orgrimmar and Ordos), 
[Seal of Tempered Fate] (for Highmaul, Blackrock Foundry, Drov the Ruiner, Tarlna the Ageless and Rukhmar) or 
[Seal of Inevitable Fate] (for Hellfire Citadel and Supreme Lord Kazzak) will afford a chance to receive a Warforged item.
Items in World of Warcraft: Legion also have a chance to be Warforged.
Patch changes
Patch 5.4.0 (2013-09-10): Added.