Formal, formality, informal or informality imply the complying with, or not complying with, some set of requirements ( forms, in

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

). They may refer to:

Dress code and events

Formal wear Formal wear or full dress is the Western dress code category applicable for the most formal occasions, such as weddings, Baptism, christenings, confirmations, funerals, Easter traditions, Easter and Christmas traditions, in addition to certain ...

, attire for formal events * Semi-formal attire, attire for semi-formal events * Informal attire, more controlled attire than casual but less than formal * Formal (university), official university dinner, ball or other event * School formal, official school dinner, ball or other event

Logic and mathematics

* Formal logic, or symbolic logic ** Informal logic, the complement, whose definition and scope is contentious * Formal fallacy, reasoning of invalid structure ** Informal fallacy, the complement * Informal mathematics, also called naïve mathematics * Formal cause, Aristotle's intrinsic, determining cause * 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 Set theory is the branch of mathematical logic that studies Set (mathematics), sets, which can be informally described as collections of objects. Although objects of any kind can be collected into a set, set theory – as a branch of mathema ...

, 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

Computer science

Formal methods In computer science, formal methods are mathematics, mathematically rigorous techniques for the formal specification, specification, development, Program analysis, analysis, and formal verification, verification of software and computer hardware, ...

, mathematically based techniques for the specification, development and verification of software and hardware systems * Formal specification, describes what a system should do, not how it should do it * Formal verification, proves correctness of a system

Linguistics

* 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 * Colloquialism, the linguistic style used for informal communication * T–V distinction, involving a distinction between formal and informal words for "you" * Formal proof, a fully rigorous proof as is possible only in a formal system * Dynamic and formal equivalence word-for-word translation, especially of the Bible

Chemistry

* Formal concentration, molar concentration of original chemical formula in solution *Formal (pronounced "form-al") **A compound CH₂(OR)₂, named in analogy to acetals CHR¹(OR)₂ (historical definition) and ketals CR¹R²(OR)₂ ** Dimethoxymethane (CH₂(OCH₃)₂) in particular, the formal derived from methanol

Social regulation

* A formality, an established procedure or set of specific behaviors ** Pro forma, for no purpose other than satisfying a formality *Informal activities: ** Informal education, education outside of a standard school setting ** Informal sector, the part of an economy that is not taxed, nor monitored by any form of government ** Informal settlement, or shanty town ** Informal value transfer system, outside the conventional banking system ** Informal social control, enforcing norms without resort to laws

Other

* Informal vote, a spoiled, void, null vote cast in an election * MV ''Formality'', coaster (formerly ''Empire Favourite'') owned by F T Everard & Sons, scrapped in 1962