Vigilance is a warrior talent available at level 75.
Tips and Tactics
Vigilance is best put on either the healer or a DPS class which produces the most threat. It helps to have Omen (or a similar threat-tracking addon) or, if the party members don't have Omen, a damage meter addon so you can determine which party or raid member is producing the most threat. This will make it so that they lose a good chunk of the threat they cause, and you gain whatever they lose. The lack of a cooldown on Taunt is useful as well, as it allows you to immediately take the mob off of the party/raid member should you lose aggro, even if you've already used Taunt in the past 6 seconds.