Omega is the twenty-fourth and last Greek letter, created by the Greeks by opening the loop of omicron to mark the long o; its name means 'great O' (o-mega) and its value is 800, the highest of the classical letter-numerals. As the last letter Omega means 'the end' or 'the last', and in the Book of Revelation it is paired with Alpha in the divine title 'the Alpha and the Omega', a genuine and well-known symbolic use.
The Greek letters doubled as numerals in the Milesian (alphabetic) system, in which each letter carried a fixed value; the practice of summing a word's letters into a number, called isopsephy, is the Greek counterpart of Hebrew gematria and appears in inscriptions, the Greek Magical Papyri and early Christian texts. Omega is one of four supplementary letters, together with Phi, Chi and Psi, added at the end of the Greek alphabet once its Phoenician-derived series had run out; its name, coined in Greek as o mega, the great O, was set deliberately against omicron, the small O, and because it was added last of all, closing the alphabet, the Book of Revelation's title the Alpha and the Omega pairs the first and last Greek letters as a figure for beginning and end. Its isopsephy value of 800 belongs to the Milesian alphabetic numeral system, which also needed three further, otherwise obsolete letters, digamma (also called stigma), koppa and sampi, to cover every value from 1 up to 900; none of the three survives among the 24 letters in ordinary use today.