Formal, formality, informal or informality imply the complying with, or not complying with, some

set Set, The Set, SET or SETS may refer to: Science, technology, and mathematics Mathematics *Set (mathematics), a collection of elements *Category of sets, the category whose objects and morphisms are sets and total functions, respectively Electro ...

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 data ...

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 peri ...

). 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 Semi-formal wear or half dress is a grouping of dress codes indicating the sort of clothes worn to events with a level of formality between informal wear and formal wear. In the modern era, the typical interpretation for men is black tie for eve ...

, 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 of fo ...

, more controlled attire than casual but less than formal *

Formal (university) Formal hall or formal meal is a meal held at some of the oldest universities in the United Kingdom and the Republic of Ireland (as well as some other Commonwealth countries) at which students usually dress in formal attire and often gowns to di ...

, official university dinner, ball or other event *

School formal A promenade dance, commonly called a prom, is a dance party for high school students. It may be offered in semi-formal black tie or informal suit for boys, and evening gowns for girls. This event is typically held near the end of the school year ...

, 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 premises ...

, 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. ...

, the complement, whose definition and scope is contentious *

Formal fallacy In philosophy, a formal fallacy, deductive fallacy, logical fallacy or non sequitur (; Latin for " tdoes not follow") is a pattern of reasoning rendered invalid by a flaw in its logical structure that can neatly be expressed in a standard logic syst ...

, reasoning of invalid structure **

Informal fallacy Informal fallacies are a type of incorrect argument in natural language. The source of the error is not just due to the ''form'' of the argument, as is the case for formal fallacies, but can also be due to their ''content'' and ''context''. Falla ...

, the complement * Informal mathematics, also called naïve mathematics * Formal cause, Aristotle's intrinsic, determining cause *

Formal power series In mathematics, a formal series is an infinite sum that is considered independently from any notion of convergence, and can be manipulated with the usual algebraic operations on series (addition, subtraction, multiplication, division, partial sum ...

, 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 Naive set theory is any of several theories of sets used in the discussion of the foundations of mathematics. Unlike Set theory#Axiomatic set theory, axiomatic set theories, which are defined using Mathematical_logic#Formal_logical_systems, forma ...

Formal derivative In mathematics, the formal derivative is an operation on elements of a polynomial ring or a ring of formal power series that mimics the form of the derivative from calculus. Though they appear similar, the algebraic advantage of a formal derivati ...

, an operation on elements of a polynomial ring which mimics the form of the derivative from calculus

Computer science

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