A generic
language where
speech is
achieved by
hand gestures rather than
sound. There are many different languages, usually one per
country, with many
dialects within each country. Sign languages are usually developed organically, largely by the
deaf community. There is, however, an
International Sign Language that is similar to
Esperanto in idea, and was specifically created.
While sign languages are used primarily by the deaf community, in fact they are useful for anybody, when speech cannot be relied upon (because of loud background noise or similar).
For further examples, see American Sign Language and British Sign Language.