Functionalism is a term in the Psychology of Language that refers to the theory that the structure of language has a basis in the communicative functions language serves.
Other /More definition:
Functionalism refers to the school of Psychology concerned with how behavior and mental abilities help people adapt to their environments; school of psychology emphasizing questions such as why the mind or a particular cognitive process works the way(s) it does. Functionalism seeks to understand what people do, and why they do it.
Moreover, Functionalism is an approach to psychology holding that the mind evolved to help us adapt to the world around us, and that the focus of psychology should be the study of those adaptive processes.
Under the influence of Darwin, the school of Functionalism stressed the role of consciousness and behavior in adapting to the environment.
List of books: Functionalism