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 Informal wear or undress, also called business wear, corporate/office wear, tenue de ville or dress clothes, is a Western dress codes, Western dress code for clothing defined by a business suit for men, and cocktail dress or pant suit for wome ...

, 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 study of deductively valid inferences or logical truths. It examines how conclusions follow from premises based on the structure o ...

, or symbolic 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 logic and philosophical logic, philosophy, a formal fallacy is a pattern of reasoning rendered validity (logic), invalid by a flaw in its logical structure. propositional calculus, Propositional logic, for example, is concerned with the meaning ...

, 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''. Fallac ...

, 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 i ...

, 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 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 deriv ...

, 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 formal grammar is a set of Terminal and nonterminal symbols, symbols and the Production (computer science), production rules for rewriting some of them into every possible string of a formal language over an Alphabet (formal languages), alphabe ...

, 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 (also called molarity, amount concentration or substance concentration) is the number of moles of solute per liter of solution. Specifically, It is a measure of the concentration of a chemical species, in particular, of a s ...

, 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 and tend ...

, 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