In the Bible's Book of Revelation, 666 is referred to as the "number of the beast". The idea of the "number of the beast" may come from gematria, a Jewish numerology practice where each letter of the Hebrew alphabet corresponds to a number. In modern popular culture, 666 has become one of the most widely recognized symbols for the Antichrist or, alternatively, the devil. Some women expressed concern about giving birth on June 6, 2006.