Chai in Hebrew means ‘alive’ or ‘living’. It is composed of two Hebrew letters- Chet and Yud. The letters also have a geometrical value of 18 – Chet having a value of 8 and Yud having a value of 10.
The number 18 is therefore considered a symbol of life and is frequently used in Jewish culture (i.e. if you give a gift that is in multiples of 18 incorporates the number 180 then it has more of a blessing). From a Kabbalistic perspective, the Chai symbol is linked to God’s attribute of ‘Ratzon’ or will, and it is a person’s will which truly defines who he is.