Near-back vowel

A near-back vowel is any in a class of vowel sound used in some spoken languages. The defining characteristic of a near-back vowel is that the tongue is positioned slightly further forward in the mouth as in a back vowel, but not as front as in a central vowel. In practice, what are analyzed phonemically as unrounded back vowels are typically near-back in their actual articulation.

Near-back vowels are sometimes called back-central, centralized back, advanced back or retracted central.

Near-back vowels are essentially a type of back vowels; no language is known to contrast a near-back vowel with a central vowel and a back vowel based on backness alone.

The only near-back vowel that has a dedicated symbol in the International Phonetic Alphabet is the near-close near-back rounded vowel [ʊ]. If precision is desired, the protruded rounding can be transcribed as ⟨u̽⟩ or ⟨ʊ⟩, whereas the compressed rounding as ⟨ʊᵝ⟩. The unrounded equivalent of this vowel can be transcribed as either ⟨ɯ̽⟩ or ⟨ɯ̞̈⟩.

Other near-back vowels can be indicated with diacritics of relative articulation applied to letters for neighboring vowels, such as ⟨u̟⟩ or ⟨ʉ̠⟩ for a close near-back rounded vowel.

...
Wikipedia