Part of the Conqueror's Battlegear set:

The set gives these bonuses as more pieces are worn: 3: Decreases the rage cost of all Warrior shouts by 35%. 5: Increase the Slow effect and damage of Thunder Clap by 50%. Set Details | All Sets

Quest Reward from:

Level	Name	Start	Rewards
60	Conqueror's Legguards  (Raid) Horde and Alliance Ahn'Qiraj	Kandrostrasz <Brood of Alexstrasza>	9950 XP

Disenchants into

Name	Value	Drop%
Nexus Crystal	1 Copper	100.0%