sign language

(countable) One of several natural languages, typically used by the deaf, in which words consist of hand shapes, motions, positions, and facial expressions.

(uncountable) The sign language (sense 1) that is used locally or that is mistakenly believed to be the only one.

(uncountable) Sign languages (sense 1) considered collectively.

(countable or uncountable) Communication through gestures as a substitute for language, for example, between monks under a vow of silence or during trade amongst different linguistic groups.