The term formal has a number of uses, including:

General

• relating to formality
• opposite of informal

Social

• Formal occasion
• Formal attire worn on such occasions
• Formals are particular meals at some British universities
• In Australian or British English, a formal is the equivalent of the American prom dance.
• In American English, a "formal" is organized by a college or university organization, typically but not always a fraternity or sorority.
• Informal occasion (included as Informal redirect here); see Dress code (Western) for the distinctions between Formal, Semi-formal, and Informal
• Informal attire (not to be confused with Casual -- see Dress code (Western))

Philosophical

• relating to form, i.e. appearance rather than essence.
• relating to Formalism, i.e. emphasis on form over content or meaning.
• formal logic logical argument based only on the form and not on the meaning.
• Formal cause, Aristotle's intrinsic, determining cause.

Mathematics

• formal power series, a generalization of power series without requiring convergence, used in combinatorics;
• formal calculation, a calculation which is systematic, but without a rigorous justification;
• formal set theory as opposed to naive set theory;
• formal derivative, an operation on elements of a polynomial ring which mimics the form of the derivative from calculus.

Logic and Language

• formal system, an abstract means of generating inferences in a formal language;
• formal language, comprising the symbolic "words" or "sentences" of a formal system;
• formal grammar, a grammar describing a formal language;
• formal proof, a fully rigorous proof as is possible only in a formal system.

Computer science

• formal methods in computer science, including:
• formal specification describes what a system should do, not how it should do it
• formal verification proves correctness of a system

See also the Language section of Mathematics, above

Linguistic

• Formal equivalence word-for-word translation (especially of the Bible)

See also the Language section of Mathematics, above

Chemical

• A unit of concentration
• short or prefix form for formalin
• short or prefix form for formaldehyde
• synonym for dimethoxymethane

See also

• Informal economy