Ge-MA-tri-a is Hebrew numerology using the Alef-bet. Each letter has a numerical value. Meaning is derived from identifying the numerical value of whole words and/or comparing the value of words and phrases to each other. Gematria is used for a deeper exploration and study of Jewish texts.
For example, the numerical value of "Chai", meaning "Life," is 18. "Chai" is spelled with a "chet," which equals 8 plus the letter "Yud" which equals 10. So the number 18 is a special number associated with the value of life.