Sign language
A sign language is one that instead of using sounds, uses combinations of handshapes, movements of the hands, arms and/or body, and facial expressions to convey information. Sign languages are most often encountered among deaf people, but American Indians were known to use a sign language to facilitate communication among tribes who spoke different languages.
Sign languages are not often written; most deaf people who use sign language read and write the spoken language of their country. However, there have been attempts at developing systems for recording sign language. Most of these have been academic attempts at transcription, which often suffer from being unable to capture all the physical features (especially the non-manual and positional ones) used by sign language. As a result they have not been used outside research. The only sign language writing system, which has been actually used by deaf people to write, is SignWriter, which rather than being developed by a linguist was devised by a dancer.
A common misconception about signed languages is that they are not real languages. Professional linguists have studied many sign languages and found them to have every linguistic component required to be classed as a true language. Sign languages are not simple pantomime and they are not a visual rendition of a simplified version of any spoken language. They have rich, complex grammars and like every other language on Earth, they can be used to discuss any topic, from the simple and concrete to the lofty and abstract. They are the linguistic equal to Chinese, English, French, or any other natural language.
Another misconception commonly held is that sign languages are dependent in some way on spoken languages, e.g. they are merely the spelling out of the words of a spoken language using gestural symbols. Although fingerspelling is used in sign languages, mostly for proper names, it is merely one tool among many. To say that sign language is not a true language because it uses fingerspelling for some things is akin to saying that English is not a true langauge because it contains onomatopoetic words. On the whole, sign languages are independent of spoken languages and they follow their own developmental paths. For example, Brittish sign language and American sign language are different and mutually unintelligible, even though the hearing people of British and America share the same spoken language. In addition, some countries that have a single spoken language throughout have two or more signed languages being used within.
Further proof of the separation of sign languages from spoken ones is the fact that sign languages exploit the unique features of the visual medium, allowing in some areas more expressivity than possible in spoken language. This is because spoken language is aural and therefore linear as only one sound can be made or received at a time, while sign languages use the visual medium where a whole scene can be taken in at once. Information can be loaded into many 'channels' and expressed simultaneously. As an illustration, one could sign a complete sentence in American Sign Language that used only ONE sign. Though only one sign is used, information about the subject, object, verb and countless ancillary and descriptive details can be packed in by altering the movement, location, speed of execution, handshape and the facial expressions incorporated in the expression of the sign to produce a sentence that could be honestly and accurately translated as: The ride here was pleasant at first but soon became treacherous as the road up the mountain was inordinately steep and circuitous with many holes in the road and fields of fallen rocks that made my arrival almost impossible and I am glad to have finally made it.
Main sign languages in use around the world today include: