Gematria is the assignment of a number to a letter, word, or phrase, often for a religious or spiritual purpose. It is used especially in the context of Judaism.
Gematria comes from the Hebrew word gematriya, a borrowing from the same Greek word that gave us geometry. Though it originated in ancient Assyria and Greece, it became a pillar of Jewish tradition used to interpret the Tanakh (Hebrew scriptures). In ancient Hebrew, there were no separate symbols for numbers, so people used letters to represent numerical values. The numerical values of the letters in a word were added up, and rabbis identified "numerical synonyms" believed to share a spiritual essence. Gematria remains a central element of the mystical tradition known as Kabbalah.