The letter "O" is the fifteenth letter of the English alphabet. It is also the fourth vowel in the English language. In the International Phonetic Alphabet, ⟨o⟩ represents the close-mid back rounded vowel. The uppercase form of the letter "O" is "O," and the lowercase form is "o". It is pronounced as /oʊ/ and has common sounds such as /ɒ/, /əʊ/, /uː/, /ʌ/, and /ə/ .