A back vowel is any in a class of vowel sound used in spoken languages. The defining characteristic of a back vowel is that the highest point of the tongue is positioned relatively back in the mouth without creating a constriction that would be classified as a consonant. Back vowels are sometimes also called dark vowels because they are perceived as sounding darker than the front vowels.
Near-back vowels are essentially a type of back vowels; no language is known to contrast back and near-back vowels based on backness alone.
The back vowels that have dedicated symbols in the International Phonetic Alphabet are:
There also are back vowels that don't 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 ⟨u̞⟩, ⟨o̝⟩ or ⟨ʊ̠⟩ for a near-close back rounded vowel.