Sign languages are languages that use the visual-manual modality to convey meaning. Sign languages are expressed through manual articulations in combination with non-manual elements. Sign languages are full-fledged natural languages with their own grammar and lexicon.
One of the most common misconceptions about sign language is that it's the same wherever you go. That's not the case. In fact, there are somewhere between 138 and 300 different types of sign language used throughout the world today. New sign languages frequently evolve amongst groups of deaf children and adults.