Meaning of ROUNDING in English
also called Labialization, in phonetics, the production of a sound with the lips rounded. Vowels, semivowels, and some consonants may be rounded. In English, examples of rounded vowels are o in note, oo in look, and the u sound in rule and boot; w in well is an example of a rounded semivowel. Unrounding is the opposite of rounding; in unrounded vowels the lips are slack or may be drawn back, as in pronouncing the ee in meet. Generally speaking, front vowels tend to be unrounded and back vowels rounded, and this tendency is recognized in the classification of vowels (see vowel). However, the French u of tu, you, in contrast with the ou of tout, all, is a high front rounded vowel; Japanese has high back unrounded vowels.
Britannica English vocabulary. Английский словарь Британика. 2012