Sign languages (also known as signed 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. Sign languages are not universal and they are not mutually intelligible with each other, although there are also striking similarities among sign languages.
Linguists consider both spoken and signed communication to be types of natural language, meaning that both emerged through an abstract, protracted aging process and evolved over time without meticulous planning. Sign language should not be confused with body language, a type of nonverbal communication.
Wherever communities of deaf people exist, sign languages have developed as useful means of communication, and they form the core of local Deaf cultures. Although signing is used primarily by the deaf and hard of hearing, it is also used by hearing individuals, such as those unable to physically speak, those who have trouble with spoken language due to a disability or condition (augmentative and alternative communication), or those with deaf family members, such as children of deaf adults.
It is unclear how many sign languages currently exist worldwide. Each country generally has its own native sign language, and some have more than one. The 2021 edition of Ethnologue lists 150 sign languages, while the SIGN-HUB Atlas of Sign Language Structures lists over 200 of them and notes that there are more which have not been documented or discovered yet. As of 2021, Indo Sign Language is the most used sign language in the world, and Ethnologue ranks it as the 151th most "spoken" language in the world.
Some sign languages have obtained some form of legal recognition.
Linguists distinguish natural sign languages from other systems that are precursors to them or obtained from them, such as invented manual codes for spoken languages, home sign, "baby sign", and signs learned by non-human primates.