In Judaism, God is known by many names. The most important of these names is the "Tetragrammaton", or "Four-lettered word": YHVH, YHWH, or י - ה וה. Jews are not allowed to say this name, and instead say "Adonai". Even "Adonai" is only used by some Jews in prayer. Most Jews would refer to God as "Hashem", or "The Name". Jews are not allowed to erase the Tetragrammaton, so they rarely write it down outside of their most holy books, such as the Torah.