A Flux is a spell used by djinn of most, if not all, types. It can be both defensive and offensive.
A Flux engulfs aggressive magic and removes it from the user's presence. Where it is taken and exactly what happens to the magic is unknown, though it is possible that the flux simply absorbs enemy magic and returns the energy to the user. Apparently, it can also be used quite rapidly, and does not require lengthy incantations or gestures. The stronger the Flux, the stronger the magic it can defend from. It is hinted that only one Flux can block one piece of magic at a time, or magic that hits the Flux at the same time. Fluxes also cover wide areas, therefore being able to span entire rooms.
It works in a different way than a golem, as a golem is so heavy with earth (the element that is strongest against demons) that it stops, deflects, or absorbs anything that it comes into contact with. Also, it might work similarly to the presence of Ramuthra, draining the magic of the attack. Or perhaps, it works similarly to the rift that brings Ramuthra to earth, and sends it back. If this is so, the flux is basically a piece of magic that sends energy back to the Other Place.