Postalveolar consonant

consonant articulated with the tongue near or touching the back of the alveolar ridge

A postalveolar consonant is a sound made with your tongue behind the alveolar ridge. For example, [ʃ] is postalveolar and [s] is not, it is alveolar.

There are only two postalveolar consonants given their own IPA symbols: [ʃ] and [ʒ].