In physics, the Greek letter omega is used to denote several things. The lowercase omega is generally used to denote angular quantities, specifically:

Capital omega is much less frequently utilised, being uncommon as a symbol for a quantity. The most common use of capital omega is as the symbol for the SI unit of resistance, the ohm.

Also, being the twenty-fourth letter in the Greek alphabet, stellar astronomers use it (along with the genitive of the constellation) to indicate the 24-th brightest star in a constellation. Thus we get Omega Centauri, Omega Orionis, Omega Cygni, etc, etc...