close, closed: Vowels are often classified by tongue height into high [1], mid [1], and low [1]. Sometimes it is necessary or useful to specify tongue-height more precisely, and the terms "close" (or "closed") and open are used for that purpose. "Close" sounds are those which are pronounced with the tongue closer to the palate (roof of the mouth) than the norm for the more general height category. (See the diagram of phonetic symbols for vowels.) The sonido [i] and sonido [u] sounds (the "ee" and "oo" sounds in "beet" and "kook"), are high close vowels, in contrast with the more open vowel sounds sonido [I] and sonido [ʊ] (which occur in "bit" and "cook"). Frequently when vowels have such small differences in height, they also have other differences, such as differences of length or tense/laxness, or diphthongization.

The description above represents the way these terms have traditionally been used by linguists in the Americas. In the European tradition represented by the International Phonetic Alphabet (see the website of the International Phonetic Association), "close" and "open" are used only with mid vowels, to distinguish the two levels mid-close and mid-open. [Spanish: cerrado]