"Each human language is a complex of knowledge and abilities enabling speakers of the language to communicate with each other, to express ideas, hypotheses, emotions, desires, and all the other things that need expressing. Linguistics is the study of these knowledge systems in all their aspects: how is such a knowledge system structured, how is it acquired, how is it used in the production and comprehension of messages, how does it change over time? "

https://linguistics.ucsc.edu/about/what-is-linguistics.html