Physicist: In a nutshell, fusion is about fusing small atoms, specifically hydrogen, together to form larger atoms, specifically helium. Cold fusion, means doing this in a controlled, consistent way on a small scale, like a power plant, as opposed to something like a bomb. The only “efficient” fusion ever attained on Earth has been in the middle of hydrogen bombs, where the fusion reaction is contained by being sandwiched between several fission explosions (several atomic bombs). With great effort, and tremendous amounts of energy (for magnets, and heating, and whatnot), you can get a little bit of fusion. However, the heat energy generated by that fusion doesn’t come close to offsetting the energy that went into getting the fusion to work in the first place.