Latin Capital Letter O

Latin Capital Letter O at U+004F is the uppercase form of the Latin letter o, used to write the vowel sound or letter name “oh” in many alphabets. It belongs to the Basic Latin block, the core set behind English text and many other Latin-script languages. In ordinary writing, it appears at the start of sentences, in proper names, acronyms, headings, and all-caps text, as in “Oxford,” “October,” or “WHO.” English uses it for several vowel sounds depending on the word, while languages such as Spanish, Italian, and German use it with more regular pronunciation patterns. It is also common as a symbol in notation: in mathematics and computer science, big-O notation describes growth rate, as in O(n) for linear time. In chemistry, O is the element symbol for oxygen, and in blood typing it names the O blood group. A practical caution is that capital O can be confused with the digit 0 in serial numbers, passwords, part codes, and license plates, especially in fonts where the shapes are very similar.