They are also known as a plosive, is an oral occlusive, a consonant in which the vocal tract is blocked so that all airflow ceases. The occlusion may be made with the tongue blade ([t], [d]) or body ([k], [ɡ]), lips ([p], [b]), or glottis ([ʔ]). Stops contrast with nasals, where the vocal tract is blocked but airflow continues through the nose, as in /m/ and /n/, and with fricatives, where partial occlusion impedes but does not block airflow in the vocal tract.
Affricates
Are consonants that begin as stops (most often an alveolar, such as [t] or [d]) but release as a fricative (such as [s] or [z] or occasionally into a fricative trill) rather than directly into the following vowel. English has two affricates, spelled ch and j.
Fricatives
Are consonants produced by forcing air through a narrow channel made by placing two articulators close together. These may be the lower lip against the upper teeth, in the case of [f]; the back of the tongue against the soft palate, in the case of German [x], the final consonant of Bach; or the side of the tongue against the molars, in the case of Welsh [ɬ], appearing twice in the name Llanelli. This turbulent airflow is called frication. A particular subset of fricatives are the sibilants. When forming a sibilant, one still is forcing air through a narrow channel, but in addition the tongue is curled lengthwise to direct the air over the edge of the teeth. English [s], [z], [ʃ], and [ʒ] are examples of this.
Two other terms are spirant and strident, but their usage is less standardized. The former can be used synonymously with "fricative", or to refer to non-sibilant fricatives only. The latter can be used synonymously with "sibilant", but some authors include also labiodental and/or uvular fricatives in the class.
Nasal
Is an occlusive consonant produced with a lowered velum, allowing air to escape freely through the nose. Examples of nasals in English are [n] and [m], in words such as nose and mouth. Nasal occlusives are nearly universal in human languages. There are also other kinds of nasal consonants in some languages.
Liquid
Liquid is a consonant produced when the tongue approaches a point of articulation within the mouth but does not come close enough to obstruct or constrict the flow of air enough to create turbulence (as with fricatives).
With liquids the air is still allowed to escape via the mouth, but its direction of flow is altered by the tongue sending it in different directions within the mouth before exiting the lips.
/l/ /r/
Glides
Is a consonant produced when the tongue approaches a point of articulation within the mouth but does not come close enough to obstruct or constrict the flow of air enough to create turbulence.
/w/ /j/
