A term coined by Luke Skywalker, the anti-Force referred to the mystical energy field which bound Waru's universe together and was the polar opposite of the Force as known by the known universe. While stranded from his own universe on board Crseih Station, Waru could only acquire the needed energy to return to his own dimension by destroying the Force of the one which held him captive with the anti-Force of his own, which he performed by draining the life forces of several sentient beings who met him during a pilgrimage to heal them of various ailments.
The anti-Force may have been present in the pocket dimension known as otherspace; one rumor within the galaxy was that former Prophet of the Dark Side Cronal accessed otherspace and used the anti-Force to facilitate his return from the dead.