Formal vs Informal Language

Definition:

Official or serious situations are often signalled by the use of formal language, while ordinary or relaxed situations are signalled by the use of informal language. Formality of language varies in relation to such factors as public v. private occasion, the size of the audience, the relationship of the speaker/writer with the audience, and so on. The ability to vary your language according to the situation is often considered a mark of an educated person.