Open front unrounded vowel
The open front unrounded vowel, or low front unrounded vowel, is a type of vowel sound, used in some spoken languages. It is one of the eight primary cardinal vowels, not directly intended to correspond to a vowel sound of a specific language but rather to serve as a fundamental reference point in a phonetic measuring system.
The symbol in the International Phonetic Alphabet (IPA) that represents this sound is ⟨a⟩, and in the IPA vowel chart it is positioned at the lower-left corner. However, the accuracy of the quadrilateral vowel chart is disputed, and the sound has been analyzed acoustically as extra-open at a position where the front/back distinction has lost its significance. There are also differing interpretations of the exact quality of the vowel: the classic sound recording of [a] by Daniel Jones is slightly more front but not quite as open as that by John Wells.
In practice, the symbol ⟨a⟩ is often used to represent an open central unrounded vowel. This is the usual practice, for example, in the historical study of the English language. The loss of separate symbols for open and near-open front vowels is usually considered unproblematic, because the perceptual difference between the two is quite small, and very few languages contrast the two. If there is a need to specify the backness of the vowel as fully front one can use the symbol ⟨æ̞⟩, which denotes a lowered near-open front unrounded vowel, or ⟨a̟⟩ with the IPA "advanced" diacritic.
Many languages have some form of an unrounded open vowel. For languages that have only a single open vowel, the symbol for this vowel ⟨a⟩ may be used because it is the only open vowel whose symbol is part of the basic Latin alphabet. Whenever marked as such, the vowel is closer to a central [ä] than to a front [a]. However, there may not actually be much of a difference. (See Vowel#Acoustics.)