Z-Neutrinos were a type of energetic particle. If compressed into a single string, Z-Neutrinos were capable of cancelling the electrical energy that held atoms together, thus decomposing matter into its base components.
The Crucible of the New Dalek Empire had a core of Z-Neutrino energy, powerful enough to tear apart a TARDIS with its defences down. Davros designed his reality bomb to use the Z-Neutrinos from the core, compressed and transmitted by the precise arrangement of 27 planets, to disintegrate matter on a universal scale.
The Meta-Crisis Tenth Doctor devised a Z-Neutrino Biological Inversion Catalyser, which would turn the energy of the Crucible against Davros and the Daleks. However, the Daleks did not give him the opportunity to use it. (TV: Journey's End)