Omega (capital: Ω, lowercase: ω; Greek Ωμέγα) 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"). This name is Byzantine; in Classical Greek, the letter was called ō (ὦ), whereas the omicron was called ou (οὖ). The form of the uppercase letter derives from that of an omicron (Ο) broken up at the side (), with the edges subsequently turned outward (, , ). The modern lowercase shape goes back to the uncial form , a form that developed during the 3rd century BC in ancient handwriting on papyrus, from a flattened-out form of the letter () that had its edges curved even further upward.
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 [ɔ], the same sound as omicron. The letter omega is transcribed ō or simply o.
In addition to the Greek alphabet, Omega was also adopted into the early Cyrillic alphabet. See Cyrillic omega (Ѡ, ѡ). A Raetic variant is conjectured to be at the origin or parallel evolution of the Elder Futhark ᛟ. Omega was also adopted into the Latin alphabet, as a letter of the 1982 revision to the African reference alphabet. It has had little use. See Latin omega.
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.