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

form Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens. Form also refers to: * Form (document), a document (printed or electronic) with spaces in which to write or enter dat ...

s, in

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

). 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 Informal wear or undress, also called business wear, corporate/office wear, tenue de ville or dress clothes, is a Western dress code for clothing defined by a business suit for men, and cocktail dress or pant suit for women. On the scale o ...

, 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 Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from premise ...

, or mathematical logic **

Informal logic Informal logic encompasses the principles of logic and logical thought outside of a formal setting (characterized by the usage of particular statements). However, the precise definition of "informal logic" is a matter of some dispute. Ralph H. J ...

, 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 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 mathematics, is mostly concer ...

, as opposed to

Naive set theory Naive set theory is any of several theories of sets used in the discussion of the foundations of mathematics. Unlike axiomatic set theories, which are defined using formal logic, naive set theory is defined informally, in natural language. It ...

* 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 mathematically rigorous techniques for the specification, development, and verification of software and hardware systems. The use of formal methods for software and hardware design is motivated by the exp ...

, 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 A formal system is an abstract structure used for inferring theorems from axioms according to a set of rules. These rules, which are used for carrying out the inference of theorems from axioms, are the logical calculus of the formal system. A for ...

, an abstract means of generating inferences in a formal language *

Formal language In logic, mathematics, computer science, and linguistics, a formal language consists of words whose letters are taken from an alphabet and are well-formed according to a specific set of rules. The alphabet of a formal language consists of s ...

, comprising the symbolic "words" or "sentences" of a formal system *

Formal grammar In formal language theory, a grammar (when the context is not given, often called a formal grammar for clarity) describes how to form strings from a language's alphabet that are valid according to the language's syntax. A grammar does not describe ...

, a grammar describing a formal language *

T–V distinction The T–V distinction is the contextual use of different pronouns that exists in some languages and serves to convey formality or familiarity. Its name comes from the Latin pronouns '' tu'' and '' vos''. The distinction takes a number of forms ...

, involving a distinction between formal and informal words for "you" *

Formal proof In logic and mathematics, a formal proof or derivation is a finite sequence of sentences (called well-formed formulas in the case of a formal language), each of which is an axiom, an assumption, or follows from the preceding sentences in the sequ ...

, a fully rigorous proof as is possible only in a formal system *

Dynamic and formal equivalence The terms dynamic equivalence and formal equivalence, coined by Eugene Nida, are associated with two dissimilar translation approaches that are employed to achieve different levels of literalness between the source and target text, as eviden ...

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 The term ''pro forma'' (Latin for "as a matter of form" or "for the sake of form") is most often used to describe a practice or document that is provided as a courtesy or satisfies minimum requirements, conforms to a norm or doctrine, tends to ...

, for no purpose other than satisfying a formality *Informal activities: **

Informal education Informal education is a general term for education that can occur outside of a structured curriculum. Informal education encompasses student interests within a curriculum in a regular classroom, but is not limited to that setting. It works through ...

, 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 In voting, a ballot is considered spoilt, spoiled, void, null, informal, invalid or stray if a law declares or an election authority determines that it is invalid and thus not included in the vote count. This may occur accidentally or deliberat ...

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