Omega is the 24th and last letter of the Greek alphabet. In the Greek numeric system, it has a value of 800. The word literally means "great O" (ō mega, mega meaning 'great'), as opposed to omicron, which means "little O" (o mikron, micron meaning "little").
In phonetic terms, the Ancient Greek Ω is a long open-mid o [ɔː], comparable to the vowel of British English raw. In Modern Greek, Ω represents the mid back rounded vowel /o/, the same sound as omicron. The letter omega is transcribed ō or simply o.
As the last letter of the Greek alphabet, Omega is often used to denote the last, the end, or the ultimate limit of a set, in contrast to alpha, the first letter of the Greek alphabet. Omega is also used in Christianity, as a part of the Alpha and Omega metaphor.