sign language

Short definition from Wiktionary

Noun

1. 1
   One of several natural languages, typically used by the deaf, in which words consist of hand shapes, motions, positions, and facial expressions.
2. 2
   The sign language (sense 1) that is used locally or that is mistakenly believed to be the only one.
3. 3
   Sign languages (sense 1) considered collectively.
4. 4
   Communication through gestures as a substitute for language, for example, between monks under a vow of silence or during trade amongst different linguistic groups.