"Ο" is the 15th letter of the Greek alphabet. It is pronounced as "omicron" and represents the vowel sound similar to the English "o" in "hot." In the Greek numeral system, it has a value of 70. In addition to its use in the Greek language, "Ο" is often found in various scientific and mathematical contexts. For example, it can represent a circle in geometry or be used as a symbol in equations. The letter is also associated with the Greek mythology figure Omicron, which is sometimes referenced in literature and art.