The voiceless glottal fricative, sometimes called voiceless glottal transition or the aspirate, is a type of sound used in some spokenlanguages that patterns like a fricative or approximantconsonantphonologically, but often lacks the usual phonetic characteristics of a consonant. The symbol in the International Phonetic Alphabet that represents this sound is ⟨h⟩, and the equivalent X-SAMPA symbol is h. However, [h] has been described as a voicelessvowel because in many languages, it lacks the place and manner of articulation of a prototypical consonant, as well as the height and backness of a prototypical vowel:
[h and ɦ] have been described as voiceless or breathy voiced counterparts of the vowels that follow them [but] the shape of the vocal tract [...] is often simply that of the surrounding sounds. [...] Accordingly, in such cases it is more appropriate to regard h and ɦ as segments that have only a laryngeal specification, and are unmarked for all other features. There are other languages [such as Hebrew and Arabic] which show a more definite displacement of the formant frequencies for h, suggesting it has a [glottal] constriction associated with its production.
An effort undertaken at the Kiel Convention in 1989 attempted to move glottal fricatives, both voiceless and voiced, to approximants. Also the approximant may be represented by the same symbol or ɦ̥.