In phonetics, vowel roundedness is the amount of rounding in the lips during the articulation of a vowel. It is labialization of a vowel. When a rounded vowel is pronounced, the lips form a circular opening, and unrounded vowels are pronounced with the lips relaxed. In most languages, front vowels tend to be unrounded, and back vowels tend to be rounded. However, some languages, such as French, German and Icelandic, distinguish rounded and unrounded front vowels of the same height, and Vietnamese distinguishes rounded and unrounded back vowels of the same height. Alekano has only unrounded vowels. In the International Phonetic Alphabet vowel chart, rounded vowels are the ones that appear on the right in each pair of vowels. There are also diacritics, U+0339 ◌̹ COMBINING RIGHT HALF RING BELOW and U+031C ◌̜ COMBINING LEFT HALF RING BELOW, to indicate greater and lesser degrees of rounding, respectively. Thus has less rounding than cardinal, and has more. These diacritics can also be used with unrounded vowels: is more spread than cardinal, and is less spread than cardinal.

Phonetics is a branch of linguistics that studies how humans produce and perceive sounds or in the case of sign languages, the equivalent aspects of sign. Linguists who specialize in studying the physical properties of speech are phoneticians. The field of phonetics is traditionally divided into three sub-disciplines based on the research questions involved such as how humans plan and execute movements to produce speech, how various movements affect the properties of the resulting sound or how humans convert sound waves to linguistic information. Traditionally, the minimal linguistic unit of phonetics is the phone—a speech sound in a language which differs from the phonological unit of phoneme; the phoneme is an abstract categorization of phones and it is also defined as the smallest unit that discerns meaning between sounds in any given language.