A language is composed of a set of visual, auditory, or tactile symbols of communication - frequently, though not always, words - which are manipulated in some way by grammar. Language can also refer to the use of such systems as a general phenomenon.
Language is considered to be an exclusively human mode of communication; although some animals may make use of quite sophisticated communicative systems, none of these are known to make use of all of the properties that linguists use to define language.
Properties of language
A set of agreed-upon symbols is only one feature of language; all languages must define the structural relationships between these symbols in a system of grammar. Implicit or explicit rules of grammar are what distinguish language from other forms of communication. They allow a finite set of symbols to be manipulated to create a potentially infinite number of grammatical utterances.
Another property of language is that its symbols are only meaningful within the language. Any meaning or grammatical rule can be attributed to any symbol. Most languages make use of sound, but the combinations of sounds used do not have any inherent meaning – they are merely an agreed-upon convention to represent a certain thing by users of that language.