Hellfire is an everlasting kind of fire, found in Bloodshadow. It cannot be extinguished. If you will find this fire, you will definitely know, it won't stop burning. If you will splash the water onto this fire, the water will decay into hydrogen and oxygen atoms.
This fire cannot be simply used. Pyrokinesis abbility cannot create the fire of this power, however, pyrokinesis still can manipulate it. With pyrokinectic instruments, some people could make weapons aka Hellfire Blade, and a expensive material, named Hell Crystal.