Formal

Formal describes adherence to established rules, conventions, or social norms. It is often contrasted with informal, casual, or improvised usage. The sense applies to language, dress, events, logic, and methods, among other domains.

In language, formality indicates level of formality in speech or writing, influenced by audience, context, and purpose. Formal language favors precise vocabulary, complete sentences, and fewer slang terms, while informal language tolerates contractions and colloquialisms. Style guides and editors often specify formality levels for different genres.

In attire and events, formal denotes dress codes such as black tie or white tie, requiring gowns or tuxedos, tailored suits, and conservative presentation. Formal occasions include weddings, state functions, and ceremonies, while the opposite is informal or casual.

In logic and mathematics, formal refers to systems defined by symbols and rules independent of external interpretation. A formal language has a precise syntax; formal proofs are constructed from axioms by inference rules. This approach underpins formal methods used to reason about systems.

In computer science and software engineering, formal methods include formal specification, modeling, and verification. They aim to prove properties such as safety and correctness of algorithms and hardware, particularly in safety-critical domains like aviation, rail systems, and medical devices.

Etymology: from Latin forma, meaning shape, appearance, or form.