Noun
LH2
Abbreviation of liquid hydrogen (a liquid composed of the liquid phase of molecular hydrogen (H2))
For instance the Saturn Vs used a lower stage powered by RP-1 (kerosene) and upper stages powered by LH2. Source: Internet
Some of the early Space Shuttle design efforts used similar designs, with one stage using kerosene into the upper atmosphere, where an LH2 powered upper stage would light and go on from there. Source: Internet