Cenarion Circle set is a type of item set. Each set consist of 3 pieces.
The Items that form those sets are quest rewards. The quests require, among other things, token drops from bosses in the Ruins of Ahn'Qiraj. Reputation with the Cenarion Circle is also required. For details, refer to the set page.
The sets consist of a weapon, a cloak and a ring, thus can be combined with almost any other set without conflicting armor slots.