E'ko

E'ko is a Zandali term referring to the life force, the spiritual power, that each creature possesses. Different creatures possess different e'ko and when one of these creatures are killed a bit of e'ko sometimes comes out. The witch doctor Mau'ari is able to make this force manifest in the form of physical items that can be collected, and knows incantations that transform e'ko into juju.

Speculation
E'ko is very likely the Zandali term for Spirit, the life force of all living creatures, similar to how pandaren call it Chi.