The open back unrounded vowel, or low back unrounded vowel, is a type of vowel sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is A. The letter is called script a because it lacks the extra hook on top of a printed letter a, which corresponds to a different vowel, the open front unrounded vowel. Script a, which has its linear stroke on the bottom right, should not be confused with turned script a, , which has its linear stroke on the top left and corresponds to a rounded version of this vowel, the open back rounded vowel.
The open back unrounded vowel is the vocalic equivalent of the pharyngeal approximant . with the non-syllabic diacritic and are used in different transcription systems to represent the same sound.
In some languages (such as Azerbaijani, Estonian, Luxembourgish and Toda) there is the near-open back unrounded vowel (a sound between cardinal and ), which can be transcribed in IPA with or .