Cold Fusion Definition
As I understand it, the normal definition of cold fusion is theoretical and involves generating thermonuclear reactions at extremely low levels so as to produce a stable and very long-lasting, low-energy power-source.
Essentially one could compare a cold-fusion, fusion-reactors, and fusion bombs in the following way
Cold Fusion: Analogous to metabolism. Energy is produced at a very low rate with a very low release of energy over a long period of time. Less energetic than a typical fusion reactor which revolves around using controlled (potentially continuous) nuclear reactions which are far more energetic.
Hot Fusion Reactor: Analogous to controlled combustion. While the energy release is quite substantial, it is controlled. Fusion reactions are highly efficient so enormous amounts of power could be generated over a long time.
Fusion Bomb: Also known as an H-Bomb. The reaction is extremely energetic and very rapid in duration. The result is an enormous surge of radiation and a massive expansion in an atmosphere. Basically a huge explosion ensues.
In the movie, the definition is not a typical definition used for cold-fusion, what they seem to be describing is some kind of endothermic reaction to absorb all the heat from the volcano to basically inert it.