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A fricative is a consonant 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 ; the back of the tongue against the soft palate in the case of German ; or the side of the tongue against the molars, in the case of Welsh. 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 , , , and are examples of sibilants.
The usage of two other terms is less standardized: "Spirant" is an older term for fricatives used by some American and European phoneticians and phonologists. "Strident" could mean just "sibilant", but some authors include also labiodental and uvular fricatives in the class.