A numeral system originating using the letters of the ancient Hebrews. There was no notation for zero, and the numeric values for individual letters was added together. Due to difficulty in transcribing hebrew letters, the names are used in this table. The page at http://www.inner.org/gematria/gemchart.htm has a picture of the letters and a alternate way of writing the letter names, or see the entry for the Hebrew alphabet. The last five letters are actually 'sofeet' forms of the hebrew letters. (there are only 22 hebrew letters, but 27 entries in the table) The sofeet form of a hebrew letter is the alternate form used when that letter is the last letter in a word.
This conversion rule for words into numbers is used in a form of hebrew mysticism called Gematria.