Sigma (upper-case Σ, lower-case σ, lower-case in word-final position ς; Greek σίγμα) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. When used at the end of a word, when the word is not all upper-case, the final form (ς) is used, e.g. (Odysseus); note the two sigmas in the center of the name, and the word-final sigma at the end.