In phonetics, consonant sounds like “f,” “s,” and “v” made by forcing air through a narrow gap are called fricatives.
The narrow opening creates turbulent airflow, producing the audible friction or hissing associated with these sounds. The exact location of the constriction determines the sound: /f/ and /v/ are made by bringing the lower lip close to the upper teeth, while /s/ is made with the tongue near the alveolar ridge behind the upper teeth. A fricative may be voiced, as /v/ is, or voiceless, as /f/ and /s/ usually are.
Fricatives differ from plosives, such as /p/, /t/, and /k/. A plosive completely blocks airflow before releasing it suddenly; a fricative maintains a narrow passage so air can continue flowing. They also differ from nasals, in which air escapes through the nose, and glides, which involve much less constriction.
The word “fricative” comes from Latin fricare, meaning “to rub,” referring to the friction-like noise created by the moving air. English also has fricatives in “sh,” “th,” and the sound in “measure.”