Wyle said:
... HHO is used instead of H2O to disguise the fact that the process is based on WATER VAPOR (ie humidity)...
As I understand it, HHO is a made-up name for a gaseous mixture of H2 and O2 molecules, in the 2-to-1 ratio that will burn completely to form water. Also nicknamed "Brown's Gas."
It should really be H2-H2-O2 but the deluded HHO enthusiasts don't seem to care about the conventions of normal chemistry or thermodynamics. You might also see the term "oxyhydrogen" but that can be applied to mixtures of H2 and O2 where the ratio is not the stoichiometric one of 2-to-1.
Wikipedia puts it very eloquently:
Fringe science and fraud
Oxyhydrogen is sometimes referred to as "Brown's Gas" after Yull Brown who claimed that it could be used as car fuel,[13][3] or "HHO gas" after the claims of fringe physicist[14] Ruggero Santilli. It mixes hydrogen and oxygen in a 2:1 molar ratio, the same proportion as water.
Oxyhydrogen is also often mentioned in conjunction with devices that claim to operate a vehicle using water as a fuel. The most common and decisive counter-argument against producing this gas on-board to use as a fuel or fuel additive is that the energy required to split water molecules exceeds the energy recouped by burning it.[15] Additionally, the number of liters per minute of gas that can be produced for on-demand consumption through electrolysis is very small in comparison to the liters per minute consumed by an internal combustion engine.[16]