Omega (Ω ω) (literally, big O) is the 24th and last letter of the Greek alphabet. In the Greek numeric system it had a value of 800.

Omega is used to denote an end to something, the opposite being Alpha, beginning. For example, "I am Alpha and Omega, the beginning and the end, the first and the last." (Revelation 22:13, KJV)

Omega has been used as the name for a wide variety of other things, for example:

• Omega is a Swiss watch company.
• In military terms, Code Omega means a situation of the highest danger and priority, the September 11, 2001 attacks being a good example.
• Omega is the name of the free 16-Bit (Unicode) version of the typesetting system TeX ([1])
• Omega is a fictional character from the television program Doctor Who.
• Omega is a fictional chemical substance from the television program Star Trek: Voyager.
• a Roguelike game ([2])
• a fatty acid: Omega-3 fatty acid
• the lowest ranking position in a group of animals (the omega (wolf) in a pack)
• a line of Omega and Omegaflex roll film cameras
• Omega was the first worldwide radio navigation system
• Omega is a Hungarian rock band.
• an optional 'superboss' present near the end of Final Fantasy V. Also a high-level mission boss in Final Fantasy XI. Final Fantasy's Omega resembles a large, mechanical, four-legged spider.

The upper-case letter Ω is used as a symbol for:

• Ohm - SI unit of electrical resistance.
• In computer science, in notation related to Big O notation, also Chaitin's constant.
• Codex Athous Dionysii, an 8th/9th century uncial Greek manuscript of the Gospels on Mount Athos.
• Omega Point, a theory about computing at the end of the universe.
• In mathematics, the first uncountable ordinal number.
• In mathematics, the Omega constant.
• Naoki Maeda's pseudonym for the Dance Dance Revolution song Max 300.

The lower-case letter ω is used as a symbol for:

• In textual criticism, the archetype of a manuscript tradition.
• In physics, angular velocity.
• In mathematics, the first transfinite ordinal number