An oral vowel is a vowel that is produced by air that escapes through the mouth only (as opposed to nasal vowels, in which air also goes out through the nose).
All languages have oral vowels; some also have nasal vowels. Sometimes the oral vowels are always phonetically oral, but often the phonemically oral vowels become nasalized when adjacent to nasal consonants. For example, the vowel /I/ in English tin is phonetically nasal [I~] due to the presence of the nasal /n/.
