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

_{2}(OR)_{2}, named in analogy to ^{1}(OR)_{2} (historical definition) and ketals CR^{1}R^{2}(OR)_{2}
** Dimethoxymethane (CH_{2}(OCH_{3})_{2}) in particular, the formal derived from methanol

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 ...

). 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, christenings, confirmations, funerals, Easter and Christmas traditions, in addition to certain state dinners, audiences, ...

, 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)
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 ...

, 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 ...

, 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, reasoning of invalid structure
** Informal fallacy, the complement
*Informal mathematics
Informal mathematics, also called naïve mathematics, has historically been the predominant form of mathematics at most times and in most cultures, and is the subject of modern ethno-cultural studies of mathematics. The philosopher Imre Lakatos in ...

, 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 s ...

, a generalization of power series without requiring convergence, used in combinatorics
*Formal calculation
Formal, formality, informal or informality imply the complying with, or not complying with, some set of requirements (forms, in Ancient Greek). They may refer to:
Dress code and events
* Formal wear, attire for formal events
* Semi-formal attir ...

, 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 de ...

*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
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 expe ...

, 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
In the context of hardware and software systems, formal verification is the act of proving or disproving the correctness of intended algorithms underlying a system with respect to a certain formal specification or property, using formal met ...

, 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 symb ...

, 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, 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 evidenc ...

word-for-word translation, especially of the Bible
Chemistry

*Formal concentration
Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of sol ...

, molar concentration of original chemical formula in solution
*Formal (pronounced "form-al")
**A compound CHacetals
In organic chemistry, an acetal is a functional group with the connectivity . Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments no ...

CHRSocial regulation

* Aformality
A formality is an established procedure or set of specific behaviors and utterances, conceptually similar to a ritual although typically secular and less involved. A formality may be as simple as a handshake upon making new acquaintances in West ...

, 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
An informal economy (informal sector or grey economy) is the part of any economy that is neither taxed nor monitored by any form of government.
Although the informal sector makes up a significant portion of the economies in developing countrie ...

, the part of an economy that is not taxed, nor monitored by any form of government
** Informal settlement
Informal housing or informal settlement can include any form of housing, shelter, or settlement (or lack thereof) which is illegal, falls outside of government control or regulation, or is not afforded protection by the state. As such, the infor ...

, or shanty town
** Informal value transfer system, outside the conventional banking system
** Informal social control Informal social control, or the reactions of individuals and groups that bring about conformity
Conformity is the act of matching attitudes, beliefs, and behaviors to group norms, politics or being like-minded. Norms are implicit, specific rule ...

, 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
See also

*Form (disambiguation)
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
* ...

* Formalism (disambiguation)
* Formal theory (disambiguation)
{{disambiguation
cs:Formální