fifteenth letter of the Greek alphabet From Wikipedia, the free encyclopedia
Omicron (uppercase/lowercase Ο ο), otherwise referred to as o for short, is a letter of the Greek alphabet. It is used to represent the short "o" sound in Ancient and Modern Greek. In the system of Greek numerals, it has a value of 70. Letters that came from it include the Roman O and Cyrillic О.
In mathematics and computer science, the uppercase Ο is used in big-O notation, while the lowercase ο is used in little-o notation (a variant of big-O notation).[1][2]