Quantum flux
From Memory Alpha, the free Star Trek reference
Quantum flux was the change of a quantum signature into an asynchronous quantum state.
All matter in the universe resonated on a quantum level. This resonation had a unique signature which could not be changed by any known process. It was the foundation of existence. Matter could be brought into a state of quantum flux by passage through a quantum fissure. In lifeforms this could be detected by examining cellular RNA which would be asynchronous with normal matter. (TNG: "Parallels")
Subspace transporters also brought matter into quantum flux. Transporter range could be extended to several light years, but Federation had abandoned its research in the field, when the technology was found to be unstable and unreliable. Bok used such a device to board the USS Enterprise-D in 2370. (TNG: "Bloodlines")
