Runeforging

Runeforging is a skill specific to death knights, involving the affixing of runes to the death knight's weapon. It requires a runeforge, which can be found in four places: The upper chamber of Acherus: The Ebon Hold in the Eastern Plaguelands, the Shadow Vault in northern Icecrown, the fortress structure at Mord'rethar: The Death Gate in southeastern Icecrown, and Darion Mograine's runeforge at Light's Hammer in Icecrown Citadel. After a small quest chain, the Shadow Vault—inhabited by hostile Scourge—can be captured to serve as a questing hub for the Knights of the Ebon Blade, allowing ease of access to the Vault's runeforges.

Process
To engrave a rune on a weapon, open your spellbook to your specialization's tab and click on the Runeforging icon. You'll see a list of Runes that you know. Choose a rune, then click the Engrave button. Your mouse pointer turns blue—use it to click on the weapon you want engraved. It helps to already have your character profile or bags open.

Details
Runeforge enchantments count as permanent, and they overwrite any regular enchantments such as Enchant Weapon - Mongoose or Enchant Weapon - Executioner. Runeforge enchantments can also be placed on Bind-to-account weapons, such as Bloodied Arcanite Reaper. Runes are always better than weapon enchantments.

Runeforging requires that the weapon have an item level of 45 or higher (except for BoA items), since any weapon a death knight would encounter will be higher than this. Prior to patch 4.0.3, attempting to apply a rune to an heirloom weapon would result in an error about the item level being too low.

Runes
As of patch 9.0.1, there are eight different runes that can be engraved onto your weapons. A weapon can only have one rune on it at a time, but runes can be freely changed at a runeforge.

Removed runes
The following runes have been removed from the game.