Chai (pronounced [xai], occasionally [ħai]) is a symbol and word that figures prominently in Jewish culture and consists of the letters of the Hebrew alphabet Het (ח) and Yod (י). In the Hebrew language, the word chai (חַי) spelled by these two letters means "living," is related to the term for "life," chaim, and also appears in the slogan "`am yisrael chai!" ("The nation of Israel lives!", referring to all Jews).

Numerological implications
There have been various mystical numerological speculations about the fact that, according to the system of gematria, the letters of chai add up to 18 (see "Jewish use of the Tetragrammaton" and "Lamedvavniks"). For this reason, 18 is a lucky number in Judaism, and many Jews give gifts of money in multiples of 18 as a result.

References in culture
The Chai symbol is often worn by Jews as a medallion around the neck (along with the Star of David (Magen David) and the Hamsa). In Hebrew, the related word chaya means living thing or animal, derived from the Hebrew word chai (חי), meaning "life". Although rare, Chai can also be used as a boy's name. Chaya, derived from chai was a popular female name in Hebrew. The name "Chaim" is quite a common boy's name, particularly among Orthodox Jews and in Israel. Among all Jews, both religious and secular, the toast "l´chaim", which means "to life", is frequently used when celebrating something, such as one of the high holidays, birthdays, weddings etc. See also the article about "Etz Chaim", meaning "tree of life" for more related information.