Nasal vowel 鼻化元音
A nasal vowel is a vowel that is produced with a lowering of the velum so that air escapes both through the nose as well as the mouth. By contrast, oral vowels are vowels without this nasalization. As explained below, nasal vowels that are distinctive or obligatory are of far more linguistic importance than whether or not speakers of a language tend to nasalize vowels in some instances. Relatively similar languages in the same branch of a language family differ on this point quite frequently throughout the world such as in Spanish and Portuguese.