In phonetics, a continuant is a speech sound produced without a complete closure in the oral cavity. By one definition, continuant is a distinctive feature that refers to any sound produced with an incomplete closure of the vocal tract, thus encompassing all sounds (including vowels) except nasals, plosives and affricates. By another definition, it refers exclusively to consonantal sounds produced with an incomplete closure of the oral cavity, prototypically approximants and fricatives, but sometimes also trills. Compare sonorants (resonants), a class of speech sounds which includes vowels, approximants and nasals (but not fricatives), and contrasts with obstruents.