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").
OmegaWiki Dictionary
Ω
omega The last letter of the modern and of the classical Greek alphabet. Uppercase version: Ω; lowercase: ω.