sign language

n. In a spoken language, a signal containing structural information is transmitted acoustically: decoded auditorily, encoded using the vocal apparatus. In a sign language, in contrast, structural information is transmitted via gestures that are decoded visually and encoded using hand shape, position, and movement, along with facial expressions and head and body position. Sign languages 
have full-fledged lexicons as well as complex grammars whose operations are based on principles subsumed under universal grammar. Signs can be combined into complex strings, as words are combined into sentences in spoken languages. Sign languages also have a prosodic component, to combine signs into phrases and separate phrases from each other, indicated by synchronous upper face markers (eyebrows, eye blinks) and head position or body orientation. – EMF

▶ See also AMERICAN SIGN LANGUAGE