Demoralizing shout is a warrior ability learned at level 56 for those with the Protection specialization. It reduces the damage done to warriors by all enemies within 10 yards for a short period of time.
Demoralizing Shout will pull non-hostile monsters and will put you into PvP mode if it hits nearby hostile players while in your own territory, so be careful with it.
Usually useful while tanking, as you want take less damage.
Brings stealthed units out of stealth if it hits them.
Obviously this skill should be used when fighting multiple mobs where its effects are multiplied. However it is even worth using against a single enemy, even one that is slightly inferior. The damage reduction is noticeable. For solo grinding on melee mobs, many warriors start off with a charge followed by demoralizing shout.