Koinoenergy is a form of energy. The finger-like extensions of the cosmic cloud encountered by the USS Enterprise in 2269 consisted of a combination of koinoenergies. (TAS: "One of Our Planets Is Missing")
Koinoenergy literally means "common energy". The "koino" prefix is sometimes used in science as a counterpart to "anti". Presumably, koinoenergy is used to distinguish from negative energy.