What is this thing called language?

What is this thing called language?

Xehetasun bibliografikoak
Egile nagusia: Nunan, David
Formatua: Liburua
Hizkuntza:English
Argitaratua: Houndmills, Basingstoke, Hants. Palgrave Macmillan 2007.
Gaiak:
Linguistics.
Grammar, Comparative and general.