'Shifting' is defined as any physical, mathematical, mental or subcultural change in one's surroundings. Essentially it's the official term (used by NPCs) for both the experimentation going on within the village, and the abilities of the Third Party NPCs, the enemies of the Malnosso, and what the barrier is protecting your characters from.
There are three types of shifts; Natural, Progressive, and Synthesized/Artificial. Natural Shifts occur outside the barrier, and are more or less unknown at the moment. Progressive Shifts are an ability of the Third Party, a natural ability of the full-winged Filial. It is extremely powerful and very dangerous in a fight, as it can alter the effects of most character actions if not properly neutralized with Artificial Shifting technology; this is what makes the Third Party so dangerous, since the neutralizing technology has only recently been created for widespread use. Artificial Shifts equate to the events and strange occurrences that take place within the barrier, and can vary in effect. It is less powerful and, to balance, less dangerous for both the world and those involved.