(from Grey's Anatomy s02e22 - Superstition)

http://en.wikipedia.org/wiki/Juju

Juju is an aura or other magical property, usually having to do with spirits or luck, which is bound to a specific object; it is also a term for the object.

Juju is also a term used to refer to energy: "Good juju" is good energy, "bad juju" is bad energy.