Median consonant

A median consonant, also known as a central consonant, is a consonant sound that is produced when air flows along the midline of the mouth over the tongue. The class contrasts with lateral consonants, in which air flows over one or both sides of the tongue.
Examples of median consonants are the voiced [alveolar fricative] and the palatal approximant. Others are the median fricatives, the median approximants, the trills, and the median flaps.
The term is most relevant for approximants and fricatives. Stops that have "lateral release" can be written in the International Phonetic Alphabet using a superscript symbol, e.g., or can be implied by a following lateral consonant, e.g.. The labial fricatives often—perhaps usually—have lateral airflow, as occlusion between the teeth and lips blocks the airflow in the center, but nonetheless they are not considered lateral consonants because no language makes a distinction between the two.
In some languages, the laterality of a phoneme may be indeterminate. In Japanese, for example, there is a liquid phoneme, which may be either median or lateral, resulting in /ro/ produced as or.