Two other terms are spirant and strident, but their usage is less standardized. The former can be used synonymously with "fricative", or (as in eg. Uralic linguistics) to refer to non-sibilant fricatives only. The latter can be used synonymously with "sibilant", but some authors include also labiodental and/or uvular fricatives in the class.
All sibilants are coronal, but may be dental, alveolar, postalveolar, or palatal (retroflex) within that range. However, at the postalveolar place of articulation the tongue may take several shapes: domed, laminal, or apical, and each of these is given a separate symbol and a separate name. Prototypical retroflexes are sub-apical and palatal, but they are usually written with the same symbol as the apical postalveolars. The alveolars and dentals may also be either apical or laminal, but this difference is indicated with diacritics rather than with separate symbols.
No language distinguishes voiced fricatives from approximants at these places, so the same symbol is used for both. For the pharyngeals and epiglottals, approximants are more numerous than fricatives. A fricative realization may be specified by adding the uptack to the letters, . Likewise, the downtack may be added to specify an approximant realization, .
(The bilabial approximant and dental approximant do not have dedicated symbols either and are transcribed in a similar fashion: . The base letters are however understood to specifically refer to the fricatives.)
In many languages, such as English, the glottal "fricatives" are unaccompanied phonation states of the glottis, without any accompanying manner, fricative or otherwise. However, in languages such as Arabic, they are true fricatives.
In addition, [ʍ] is usually called a "voiceless labial-velar fricative", but it is actually an approximant. True doubly-articulated fricatives may not occur in any language; but see voiceless palatal-velar fricative for a putative (and rather controversial) example.
Ubykh may be the language with the most fricatives (twenty-seven in all), some of which do not have symbols or diacritics in the IPA. This number actually outstrips the number of all consonants in English (which has 24 consonants). By contrast, approximately 8.7% of the world's languages display no phonemic fricatives at all . This is a typical feature of Australian Aboriginal languages, where the few fricatives that exist result from changes to plosives or approximants, but also occurs in some indigenous languages of New Guinea and South America that have especially small numbers of consonants. However, whereas [h] is entirely unknown in indigenous Australian languages, most of the other languages without true fricatives do have [h] in their consonant inventory.
Voicing contrasts in fricatives are largely confined to Europe, Africa and Western Asia. Languages of South and East Asia, such as the Dravidian and Austronesian languages, typically do not have such voiced fricatives as [z] and [v] which are very familiar to European speakers. These voiced fricatives are also relatively rare in indigenous languages of the Americas. Overall, voicing contrasts in fricatives are much rarer than in plosives, being found only in about a third of the world's languages as compared to 60 percent for plosive voicing contrasts.
About 15 percent of the world's languages, however, have unpaired voiced fricatives, i.e. a voiced fricative without a voiceless counterpart. Two-thirds of these, or 10 percent of all languages, have unpaired voiced fricatives but no voicing contrast between any fricative pair.
This phenomenon occurs because voiced fricatives have developed from lenition of plosives or fortition of approximants. This phenomenon of unpaired voiced fricatives is scattered throughout the world, but is confined to nonsibilant fricatives with the exception of a couple of languages which have [ʒ] but lack [ʃ]. (Relatedly, several languages have the voiced affricate [dʒ] but lack [tʃ].) The fricatives which occur most often without a voiceless counterpart are, in order of ratio of unpaired occurrences to total occurrences, [ʝ], [β], [ð], [ʁ] and [ɣ].