A language is a set of symbols bound by a set of rules which is known as the grammar and each symbol represents a specific sound or gesture. There are thousands of human languages which have evolved naturally from as far back in time as two million years according to some estimates, though this is a matter of debate. There are also constructed languages which are man-made for a specific purpose that may have similarities to natural languages, or may be completely original.
The symbols are arbitrary in that what a set of symbols, or a word, means in one language is not necessarily what it means in another. The study of language is called linguistics, which classifies languages according to the genetics, grammar and geography.
The genetics of a language refers to the family it belongs to and this depends on the ancestry of it. Families are Indo-European, Afro-Asiatic, Austronesian, and Sino-Tibetan. The structure or grammar of the language is classified according to the word order or the position of the subject, verb and object. Areal features in language classification refer to the characteristics shared by languages not because of any genetic similarities but due to the fact that the speakers of each live closely to each other and so, over time, the languages have developed common features.
The oldest surviving grammar was the classification of the Tamil alphabet into vowels and consonants in 200 BC. In 5BC, a grammarian called Panini in North India classified Sanskrit morphology into 3959 rules of grammar and was the first known linguist to develop the concepts of the phoneme, morpheme and the root of the words. In the Middle East in 760AD, a Persian linguist called Sibawayh distinguished between phonetics, or the study of the physical speed sounds, and phonology which is the study of how the sounds function within a language.