That name he used, they aren't really sure how to pronounce it but it was attempting to use the 4 letter Hebrew word they used for G-d in the Temple.
(The name of G-d is discussed in this post so please don't print it)
The high priests had bells sewn onto their clothes and a rope tied around their leg so if they DIED while saying the Name, they'd know and could pull them out.
Judaism clearly recognizes the existence of a Name for G-d (we have many Names for G-d in the Hebrew).
The most important of G-d's Names is the four-letter Name represented by the Hebrew letters Yod-Heh-Vav-Heh (Hashem). It is often referred to as the Ineffable Name, the Unutterable Name or the Distinctive Name. You'll see the word Hashem, Adonai, or G-d in it's place in most English translations.
In Deut. 12:3, the people are commanded that when they take over the promised land, they should destroy all things related to the idolatrous religions of that region (like a mosque *cough*), and should utterly destroy the names of the local deities. Immediately afterwards, we are commanded not to do the same to our G-d. From this, the Rabbis logically inferred that we are commanded not to destroy any holy thing, and not to erase or deface a Name of G-d.
(FYI this prohibition against erasing or defacing Names of G-d applies only to Names that are written in some kind of permanent form, and recent rabbinical decisions have held that writing on a computer is not a permanent form but, once you print the document out, it becomes a permanent form.)
Some Rabbis asserted that a person who pronounces Hashem according to its letters (instead of using a substitute) has no place in the World to Come, and should be put to death.
