sign language

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A language that uses a system of manual, facial, and other body movements as the means of communication, especially among deaf people.
• noun A method of communication, as between speakers of different languages, that uses hand movements and other gestures.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable One of several natural languages, typically used by the deaf, where the words and phrases consist of hand shapes, motions, positions, and facial expressions.
• noun uncountable The sign language (sense 1) that is used locally or that is mistakenly believed to be the only one.
• noun uncountable Sign languages (sense 1) considered collectively.
• noun countable or uncountable Communication through gestures used when speech is impossible, for example, between monks under a vow of silence or people speaking different languages.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun language expressed by visible hand gestures