n phonetics, an r-colored or rhotic vowel (also called a retroflex vowel, vocalic r, or a rhotacized vowel) is a vowel that is modified in a way that results in a lowering in frequency of the third formant. R-colored vowels can be articulated in various ways: the tip or blade of the tongue may be turned up during at least part of the articulation of the vowel (a retroflexarticulation) or the back of the tongue may be bunched. In addition, the vocal tract may often be constricted in the region of the epiglottis.
R-colored vowels are rare, occurring in less than one percent of the languages of the world. However, they occur in two of the most widely spoken languages: North American English and Mandarin Chinese. In North American English, they are found in words such as butter, nurse and, for some speakers, start. They also occur in Quebec French, in some varieties of Brazilian Portuguese and some Jutlandic dialects of Danish.