Page "Manner of articulation" Paragraph 22

Manners of articulation with substantial obstruction of the airflow ( stops, fricatives, affricates ) are called obstruents.

These are prototypically voiceless, but voiced obstruents are extremely common as well.

Manners without such obstruction ( nasals, liquids, approximants, and also vowels ) are called sonorants because they are nearly always voiced.

Voiceless sonorants are uncommon, but are found in Welsh and Classical Greek ( the spelling " rh "), in Standard Tibetan ( the " lh " of Lhasa ), and the " wh " in those dialects of English that distinguish " which " from " witch ".