The Tetragrammaton reference article from the English Wikipedia on 24-Apr-2004
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Tetragrammaton

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The Tetragrammaton, literally means the four-letter word. The word in question is the Hebrew word יהוה spelled using the Hebrew alphabet: yodh י heh ה waw ו heh ה. (Note that Hebrew text is written from right to left). This is the ineffable name of God in Hebrew, and is so holy that observant Jewish people read it as "Adonai" which means "My Master" in their prayers and when learning and studying the Torah or Talmud. When they want to refer to the name in conversation or in a non-textual context such as in a book, newspaper or letter, they call the name "Hashem" which means simply "The Name".

A reading from the Tanakh when Moses was faced with the burning bush on Mount Sinai, translates the Tetragrammaton as I am what I am or I shall prove to be what I shall prove to be.(Exodus 3:13) Because of the strictures in Judaism, the pronunciation is controversial.

See Yahweh and The name of God in Judaism. See also four-letter word.