The Hebrew word CHAI, (spelled Chet Yud) means life. It is also typically used to indicate the number 18, due to the fact that the numerical value of the letters is 18. It is considered auspicious, therefor, to give gifts at weddings and Bar Mitzvahs of, or in multiples of 18. This also hold true of giving gifts to charity, and in almost any Orthodox Synagogue, when the have a charity auction for various honors that will be given out in synagogue, such as who hold the Sefer Torah on Simchat Torah, the amounts are counted in multiples of Chai ("Do I hear 10 Chai? 10 Chai going once...") This word is also the root of the word L'Chaim, a traditional Jewish toast (meaning "To life")