An obstruent is a consonant sound formed by obstructing airflow, causing increased air pressure in the vocal tract, such as [k], [d͡ʒ], and [f]. In phonetics, articulation may be divided into two large classes: obstruents and sonorants.
Obstruents are those articulations in which there is closure of the vocal tract, stopping or interfering with airflow. They are subdivided into stops: p, t, k, b, d, g, with complete occlusion of the vocal tract, often followed by a release burst; fricatives, with limited closure, not stopping airflow but interfering with it and making it turbulent, called frication; and affricates, which begin with complete occlusion but then release into a fricative-like release. Obstruents are prototypically voiceless, though voiced obstruents are common. This contrasts with sonorants, which are much more rarely voiceless.