Temporal flux placed an object out of alignment with the spacetime continuum, either naturally or artificially. It could also cause that object to be temporally displaced.
Doctor Samantha Delaney's temporal weapon's beam fired in a state of temporal flux, which meant it could easily penetrate standard Starfleet deflector shields. The Dark Starship itself seemed to be in a state of constant temporal flux as well, which made it difficult to disable. (Star Trek: The Cantabrian Expeditions)
The Kartaali Star Navy used transphasic torpedoes which also could be triggered into a state of temporal flux. (Star Trek: The Cantabrian Expeditions: "Howl")