Answer:
   
   In Judaism God has several names. The most important name of God is
   the Tetragrammaton, YHVH. Because Jews considered it sinful to
   pronounce, the correct pronunciation of this name was forgotten -- the
   original Hebrew texts only included consonants. Some conjecture that
   it was pronounced "Yahweh". The Hebrew letters are named
   Yod-Heh-Vav-Heh.
   
   Jews also call God Adonai, or "my Lord." Since pronouncing YHVH is
   considered sinful, Jews would use Adonai instead in prayers. When the
   Masoretes added vowel pointings to the text of the Tanach in the first
   century CE they gave the word YHVH the vowels of Adonai, to remind the
   reader to say Adonai instead. Many Christian bible translators
   misinterpreted this to mean that God's name was Jehovah, which is the
   result of combining Adonai's vowels with YHVH's consonants, written
   using Latin orthography in which "J" is prnounced as the English "Y."
   
   All denominations of Judaism teach that the four letter name of God,
   YHVH, is forbidden to be uttered except by the High Priest, in the
   Temple. Since the Temple in Jerusalem is no longer extant, this name
   is never pronounced in religious rituals by Jews. Orthodox Jews never
   pronounce it for any reason. Some non-Orthodox Jews are willing to
   pronounce it, but for educational purposes only, and never in causal
   conversation or in prayer. Instead of pronouncing YHVH during prayer,
   Jews say "Adonai".
   
   Jews often build "fences" around the basic laws, so that there is no
   chance that the main law will ever be broken. As such, it is common
   Jewish practice among to restrict the use of the word "Adonai" to
   prayer only. In conversation many Jewish people will call God
   "HaShem", which is Hebrew for "the Name". Many Jews also write "G-d"
   instead of "God". While these substitutions are by no means required
   by Judaism (only the Hebrew name, not the English, is holy), they do
   it to remind themselves of the holiness attached to God's name.
   
   English translations of the Bible generally render YHVH as "LORD" (in
   small capitals), and Adonai as "Lord" (in normal case). Scholars
   disagree as to the meaning of the name Yahweh - many believe it means
   something like "I am the One Who Is," or "I am that I am, and I cause
   what is."
   
   Other Jewish names of God include:
     * Adonai Emet (Truth)
     * Tzur Yisrael (The Rock of Israel)
     * Elohei Avraham, Yitzchak v'Ya'acov (God of Abraham, God of Isaac,
       God of Jacob)
     * Ehiyeh sh'Ehiyeh (I Am That I Am)
     * Avinu Malkeinu (Our Father, our King)
     * Ro'eh Yisrael (Shepherd of Israel)
     * Ha-Kadosh, Baruch Hu (The Holy One, Praised be He)
     * Melech ha-M'lachim (The King of Kings)
     * Makom (literally, the Place; means "The Omnipresent")
     * Magen Avraham (Shield of Abraham)
       
   There is more information in answer [5]12.24