Energy
Green hydrogen
Green hydrogen is hydrogen produced by splitting water with renewable electricity, so its production adds no fossil carbon. The same molecule made from natural gas, which is how almost all hydrogen is made today, is called grey hydrogen.
The colour naming describes the source of the energy, not the gas, which is identical in every case.
It matters for industries that cannot be run on electricity directly, such as fertiliser and steel, rather than for uses where a wire would do.