Fricatives are consonants produced by forcing air through a narrow channel made by placing two articulators close together.[1] 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.[2]

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.[1] English [s], [z], [ʃ], and [ʒ] 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.[3] "Strident" could mean just "sibilant", but some authors[who?] include also labiodental and uvular fricatives in the class.