Righteous Fury is a paladinability, learned at level 12. It greatly increases the threat generated by all of the paladin's spells and attacks, and remains until canceled or until the paladin changes spec.
This is an ability used while tanking. It causes your actions to threaten targets and other enemies more than you usually would, which forces them to attack you instead of more fragile players you might be playing with.
This increases the threat generated by all your spells and attacks, including healing.
The value of increased threat is 400% according to.[1]
Hotfix (2011-08-16):Threat generation for all tanks has been increased to 500%, up from 300%. This applies to warriors in Defensive Stance, death knights in Blood Presence, druids in Bear Form, and paladins with Righteous Fury.
Patch 4.1.0 (2011-04-26): Now persists through death.
Hotfix (2011-01-03):Righteous Fury is now unable to be dispelled.
Patch 4.0.1 (2010-10-12): New tooltip. Is no longer restricted to increasing threat by Holy spells, nor affected by any talents. Also generates more aggro, up from +90%.
Patch 3.2.2 (2009-09-22): The bonus threat from Holy spells caused by this talent has been reduced from 90% to 80%.
Patch 3.2.0 (2009-08-04): No longer has a duration, remaining until cancelled or death. Also cancelled when a Paladin activates a different talent specialization.
Patch 2.3.2 (2008-01-08): This spell will no longer cost twice the listed mana to cast.