Mists of Pandaria - patch 5.0.1
Trillium Ore was introduced in Mists of Pandara. It comes in two flavors, White Trillium Ore and Black Trillium Ore. In order to smelt a Trillium Bar you will need some of each. Trillium Ore will spawn in the high end zones. Maps and routes are not yet available for Trillium Ore, but as the expansion gets closer to release there will be a Trillium Ore Mining Guide made available to you on a map below.
You will need a mining skill of 600 to be able to mine Trillium Ore. It is comparable to what Pyrite Ore was in Cataclysm or Titanium Ore in Wrath of the Lich King. It is the high end ore for Mists of Pandaria.
If you’re looking for information on Leveling your Mining see my WoW Mining Guide.