Back vowel

Back vowels are a class of vowel sound used in spoken languages that are produced when the tongue is positioned toward the back of the mouth. Back vowels appear in most of the world's languages, with and being present in 88% and 60% of languages according to PHOIBLE.
Back vowels are typically rounded, meaning that the lips are engaged while speakers are producing them, but can be unrounded as well. This is because languages want to maximize the degree of contrast between vowels. Rounding has the effect of bringing a vowel further back in the mouth, so across the world's languages, it's more common for back vowels to be rounded than unrounded, and for front vowels to be unrounded rather than rounded. This is reflected in the position of unrounded back vowels on the IPA vowel chart. They are written to the left of the unrounded front vowels to note that they are typically centralized.

Articulation

In their articulation, back vowels do not form a single category, but may be either raised vowels such as or retracted vowels such as.

Partial list

The back vowels that have dedicated symbols in the International Phonetic Alphabet are:

There also are back vowels that do not have dedicated symbols in the IPA:

As here, other back vowels can be transcribed with diacritics of relative articulation applied to letters for neighboring vowels, such as, or for a near-close back rounded vowel.