omicron

Omicron is the fifteenth letter of the Greek alphabet. In uppercase it is written Ο and in lowercase ο. The name derives from the phrase o mikron, meaning "small o," in contrast to omega, meaning "large o." The letter represents a close-mid back rounded vowel /o/ in Greek phonology, a value that has remained relatively stable in Modern Greek compared with other phonetic changes over time.

In Greek numerals, omicron has the value 70. It is widely used in scholarly and scientific contexts as a letter to denote variables, labels, or parameters, as is common with Greek letters in mathematics, physics, linguistics, and astronomy. In modern usage, omicron appears as part of the Greek alphabet for writing the language and as a symbol in technical notation. As a character in digital text, lowercase omicron has the Unicode code point U+03BF and uppercase Omicron U+039F.

In public naming, the World Health Organization assigned the name Omicron to the SARS-CoV-2 variant designated B.1.1.529 in 2021, following the Greek-letter naming scheme intended to avoid geographic stigma. The designation has led to omicron becoming widely recognized beyond linguistic contexts.

The term may also appear in other specialized uses, including brand names or product designations, but the primary reference remains the letter of the Greek alphabet.