The sacred name of God as revealed to Moses in the Torah is YHWH.
The name of God is critically important to Jewish beliefs. Since ancient Hebrew was written without vowels, it is not know what the original pronunciation of this word. The common pronunciation "Jehovah," however, is imprecise. It is derived from combining the vowels for Adonai ("Lord") with the four consonants of YHWH. A more "correct" pronunciation, and that which is used among scholars, is "Yahweh."
The discussion is irrelevant to observant Jews, however, as they do not pronounce this holiest of names. When the Torah is read aloud, Adonai ("Lord") is read in its place. This practice is reflected in most English translations, in which YHWH is rendered "LORD." Jews also refer to God as Hashem, "the Name."
The word YHWH is sometimes referred to as the Tetragrammaton, from the Greek for "four-lettered." It is also called "The Forbidden Name" or the "Unutterable Name." The prohibition against pronouncing this name does not originate with the command to not take the Lord's name in vain, as is sometimes thought.
Although traditionally this only applies to the Name in Hebrew, some modern Jews also refrain from writing the word "God," replacing it instead with "G-d." Opinions vary within Judaism as to the necessity of such a practice.