Greek Capital Letter Omicron Ο

The Greek Capital Letter Omicron character (Ο) is a standard HTML entity defined in the HTML specification. In HTML source code, it can be written using the named entity reference Ο, the decimal numeric character reference Ο, or the hexadecimal numeric reference Ο. The character is assigned Unicode code point U+039F in the Universal Character Set.

Greek capital omicron is visually identical to the Latin capital letter O. It is the ancestor of the Latin O and is used primarily in Greek text. In computer science, Big O notation uses the Latin O, not Greek omicron, despite the visual identity.

Greek letter entities are indispensable for scientific papers, engineering documentation, statistical analyses, and mathematical content published on the web. From physics equations using alpha and omega to statistical formulas featuring sigma and mu, these entities allow content authors to include Greek characters reliably without requiring specialized fonts or complex Unicode input methods on the keyboard.

When deciding how to encode the Greek Capital Letter Omicron character in your HTML documents, the named entity Ο is generally the most readable choice for developers reviewing or maintaining source code. The decimal form Ο and hexadecimal form Ο are equally valid alternatives that work in contexts where named entities may not be supported, or when generating HTML output programmatically from server-side code. All three representations produce identical visual output in every modern web browser.

Use the capital omicron entity in Greek-language text and alphabet displays. Big O notation in computer science (O(n), O(n²)) uses the Latin letter O, not Greek omicron, though they appear identical. Context makes the distinction clear.