hydrogen burning

In astrophysics, hydrogen burning (or hydrogen fusion) is fusion of hydrogen nuclei. References to hydrogen burning often mean proton-proton chain (PP-chain), but it may sometimes be intended to include the CNO cycle, or potentially deuterium fusion (deuterium burning). Common use of the term is to define the lower limit of a main sequence star: that it is large enough to develop sufficient temperature at the core to trigger ¹H fusion (for which PP-chain would be the first reaction to occur).

Outside of astrophysics, hydrogen burning is more likely to refers to the chemical process: in the presence of oxygen and at a sufficient temperature, they chemically combine to form water molecules.