Language is a term most commonly used to refer to so called "natural languages" — the forms of communication considered peculiar to humankind. By extension the term also refers to the type of human thought process which creates and uses language. Essential to both meanings is the systematic creation, maintenance and use of systems of symbols, which dynamically reference concepts and assemble according to structured patterns to communicate meaning. The scientific study of language is called linguistics.

A language is a system of signs (symbols, indices, icons) for encoding and decoding information. Since language and languages became an object of study by ancient grammarians, the term has had many and different definitions. The English word derives from Latin lingua, "language, tongue," "tongue," a metaphor based on the use of the physical organ in speech. The ability to use speech originated in remote prehistoric times, as did the language families in use at the beginning of writing. The processes by which they were acquired were for the most part unconscious.

In modern times, a large number of artificial languages have been devised, requiring a distinction between their consciously innovated type and natural language. The latter are forms of communication considered peculiar to humankind. Although some other animals make use of quite sophisticated communicative systems, and these are sometimes casually referred to as animal language, none of these are known to make use of all the properties that linguists use to define language.

The term “language” has branched by analogy into several meanings. The most obvious manifestations are spoken languages such as English or Spoken Chinese. However, there are also written languages and other systems of visual symbols such as sign languages. In cognitive science the term is also sometimes extended to refer to the human cognitive facility of creating and using language. Essential to both meanings is the systematic creation and usage of systems of symbols, each pairing a specific sign with an intended meaning, established through social conventions.

In the late 19th century Charles Sanders Peirce called this pairing process semiosis and the study of it semiotics. According to another founder of semiotics, Roman Jakobson, the latter portrays language as code in which sounds (signantia) signify concepts (signata). Language is the process of encoding signata in the sounds forming the signantia and decoding from signantia to signata.

Concepts themselves are signantia for the objective reality being conceived. When discussed as a general phenomenon then, "language" may imply a particular type of human thought that can be present even when communication is not the result, and this way of thinking is also sometimes treated as indistinguishable from language itself. In Western philosophy, language has long been closely associated with reason, which is also a uniquely human way of using symbols. In Ancient Greek philosophical terminology, the same word, logos, was a term for both language or speech and reason, and the philosopher Thomas Hobbes used the English word "speech" so that it similarly could refer to reason, as presented below.