Retroflexion

Retroflex
◌˞
◌̣
◌̢

A retroflex consonant is a coronal consonant where the tongue has a flat, concave, or even curled shape, and is articulated between the alveolar ridge and the hard palate. They are sometimes referred to as cerebral consonants, especially in Indology. Other terms occasionally encountered are domal and cacuminal.

The Latin-derived word retroflex means "bent back"; some retroflex consonants are pronounced with the tongue fully curled back so that articulation involves the underside of the tongue tip (subapical). These sounds are sometimes described as "true" retroflex consonants. However, retroflexes are commonly taken to include other consonants having a similar place of articulation without such extreme curling of the tongue; these may be articulated with the tongue tip (apical) or the tongue blade (laminal).

Retroflex consonants, like other coronal consonants, come in several varieties, depending on the shape of the tongue. The tongue may be either flat or concave, or even with the tip curled back. The point of contact on the tongue may be with the tip (apical), with the blade (laminal), or with the underside of the tongue (subapical). The point of contact on the roof of the mouth may be with the alveolar ridge (alveolar), the area behind the alveolar ridge (postalveolar), or the hard palate (palatal). Finally, both sibilant (fricative or affricate) and nonsibilant (stop, nasal, lateral, rhotic) consonants can have a retroflex articulation.

...
Wikipedia