Circle of Ossus

Source
This item is sold by the following vendors for :
 * in Dalaran
 * in Dalaran
 * in Icecrown Citadel
 * in Dalaran

Trivia
The Real-Time Strategy Game Age of Empires III also had a Circle of Ossus. In this game, the Circle of Ossus was an evil organization seeking the Fountain of Youth.

This item could also be a reference to Ossus, a planet in the Star Wars universe where the Jedi kept the sum of their knowledge.