In the
Old Testament, the god of the Children of Israel (later the
Jews) had a name which was supposedly unknown. It was represented by an unpronouncable four-
consonant sstring, which transliterates roughly into the
Roman alphabet as JHVJ or
YHWH. These are the origins of the names "Jehovah" and "Yahweh," although it's been pointed out that it may just as likely have been pronounced "Yahoo-Wahoo."
This
tetragrammaton is considered sacred and powerful by esoteric offshoots of
Judeo-Christianity, such as
quaballah. There is a belief among some that if it is ever pronounced the world will come to an end. This was represented to the public in
Arthur C. Clarke's mediocre (in my opinion) story the
Nine Billion Names of God.