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" (o mega, mega meaning
'great').
Omega (the last letter of the Greek alphabet) 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".
The ohm — SI unit of electrical resistance.
In astronomy (cosmology) O refers to the density of the universe, also called the density parameter.