What is "back vowel"

n. (context phonetics English) Any vowel sound produced in the back of the mouth. Examples: "u" in “rule” and "o" in “pole”

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 tongue is positioned as far back as possible 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.