Liquid consonants, or liquids, are approximant consonants that are not classified as semivowels (glides) because they do not correspond phonetically to specific vowels (in the way that, for example, the initial [j] in English yes corresponds to [i]).
The class of liquids can be divided into lateral liquids and rhotics. Obstruent laterals, which are mainly found in indigenous languages of North America and include such sounds as the voiceless alveolar lateral fricative ([ɬ]), the voiced alveolar lateral fricative [ɮ], and the affricates [tɬ], [tɬʼ], and [dɮ], are sometimes thought of as liquids but do not have their high sonority. Nor can obstruent laterals be used in the same way as sonorant laterals in the languages where they occur.
Typical liquids in English are the sounds /l/ and /ɹ/. In most other European languages the letter r represents an alveolar trill, which is its value in the IPA. In French, German and Danish, the letter r represents a uvular trill pronounced far back in the throat ([ʁ])—this may also be a uvular fricative or approximant.
Elsewhere in the world, two liquids of the types mentioned above remains the most common attribute of a language's consonant inventory, except in North America and Australia. In North America, a majority of languages do not have rhotics at all and there is a wide variety of lateral sounds - though most are obstruent laterals rather than liquids. Most indigenous Australian languages are very rich in liquids, with some having as many as seven distinct liquids. These typically include dental, alveolar, retroflex and palatal laterals, and as many as three rhotics. This richness in liquid consonants in a sense compensates for the small vowel inventories and lack of fricatives of Aboriginal languages.
Some African languages also contrast two rhotics, usually a trill and a flap.
On the other side, there are many indigenous languages with no liquids in the Amazon Basin and eastern North America, and also a few in Asia and Africa. Polynesian languages typically have only one liquid, which may be either a lateral or a rhotic.