Omega (uppercase Ω, lowercase ω) 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 letter derives from a double omicron, which came to be written open at the top.
Phonetically, the Ancient Greek Ω is a long o, similar to the vowel of English ocean. For example, the English ocean, derives from the Greek ωκεανός. It is transcribed ō or simply o. In Modern Greek Ω also sounds like a long o, though not so clear in everyday speech.
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. In the New Testament book of Revelation, God is declared to be the "Alpha and Omega, the beginning and the end, the first and the last".
Omega was also adopted into the early Cyrillic alphabet. See omega (Cyrillic) (Ѡ, ѡ). A Raetic variant is at the origin of Elder Futhark ᛟ.