The voiceless glottal fricative, sometimes called voiceless glottal transition or the aspirate,[1][2] is a type of sound used in some spoken languages that patterns like a fricative or approximant consonant phonologically, but often lacks the usual phonetic characteristics of a consonant.

However, [h] has been described as a voiceless phonation 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.

[3]An effort undertaken at the Kiel Convention in 1989 attempted to move glottal fricatives, both voiceless and voiced, to approximants.