In Hebrew, each letter has a numerical value. The number 10 is the letter Jud ( י). The number 8 is the letter Ched ( ח ). Ched-Jud spells the word Chai
(חי), which is both a word and a symbol meaning "life".
You're probably familiar with the standard Jewish toast, "L'Chaim!" - "To life!" This saying is also said at celebrations in anticipation of all the good things to come.
Judaism is a religion that emphasizes the importance of life and the hope it supports. Therefore, 18 is a popular number that represents luck. At weddings, bar mitzvahs, and honorific donations, Jews often give monetary gifts in multiples of 18, symbolically bestowing "life" or happiness on the recipient.
