One of the most significant words in Kabbalah is the ineffable name for god, (Yod, He, Vav, He), known as the Tetragrammaton.
Gematria involves calculating a numerical value for a word or phrase. In mystic traditions like Kabbalah, various value tables have been recorded that associate each Hebrew letter with its numeric counterpart (e.g. Aleph=1, Bet=2, Yud=10, etc). Read articles about gematria below.