| A Hebrew word for God (see Hebrew words for God for some history of this and other words). Literally, it means merely "the name", and is used instead of saying "Adonai", which is used instead of saying the literal name "YHWH".
The form YHWH is never uttered or written (except if writing a Bible). The form Adonai should be uttered when reading the Bible, praying or blessing, but not under other circumstances (it is written in prayer books, but not if you're handing in a class paper). The form ha-shem is what observant Jews say instead of these 2 words. But it, too, is never written down when referring to God. There is, of course, no problem to write it down or say it when one wishes to say "the name". | 
