A representation is something that is intimately "related" to something else, so that one can say that it represents it.

In Computer science, representation is crucial, because Information needs to represent something else to have Meaning, by definition. This meaning, is what makes Minds and computers "think" and be useful and not just process meaningless information (which they also do).

Art: Design, Medium, Communication

Mathematical formalisms: Coding theory, Information theory

Philosophy: Language and meaning, Philosophy of mind.