Jade Druid is an archetype that was created with the release of Mean Streets of Gadgetzan. While three classes have access to jade cards, it was Druid with its mana acceleration and the class card Jade Idol that benefited the most from the new keyword.
The archetype has had periods of dominance, and in particular was very powerful early in the Knights of the Frozen Throne expansion release. This led to the nerf of Innervate and Spreading Plague. The deck got weaker, but continues to be a solid option for anyone headed to the ladder.