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 ( 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 A promenade dance or prom is a formal dance party for graduating high school students at the end of the school year. Students participating in the prom will typically vote for a ''prom king'' and ''prom queen''. Other students may be honored w ...

, 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 The four causes or four explanations are, in Aristotelian thought, categories of questions that explain "the why's" of something that exists or changes in nature. The four causes are the: material cause, the formal cause, the efficient 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 su ...

, a generalization of power series without requiring convergence, used in combinatorics *

Formal calculation In mathematical logic, a formal calculation, or formal operation, is a calculation that is ''systematic but without a rigorous justification''. It involves manipulating symbols in an expression using a generic substitution without proving that the ...

, 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 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 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 In computer science, formal specifications are mathematically based techniques whose purpose is to help with the implementation of systems and software. They are used to describe a system, to analyze its behavior, and to aid in its design by verify ...

, 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 a system with respect to a certain formal specification or property, using formal methods of mathematics. Formal ver ...

, proves correctness of a system

Linguistics

Formal system A formal system is an abstract structure and formalization of an axiomatic system used for deducing, using rules of inference, theorems from axioms. In 1921, David Hilbert proposed to use formal systems as the foundation of knowledge in ma ...

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

Formal language In logic, mathematics, computer science, and linguistics, a formal language is a set of strings whose symbols are taken from a set called "alphabet". The alphabet of a formal language consists of symbols that concatenate into strings (also c ...

, 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 Colloquialism (also called ''colloquial language'', ''colloquial speech'', ''everyday language'', or ''general parlance'') is the linguistic style used for casual and informal communication. It is the most common form of speech in conversation amo ...

, the linguistic style used for informal communication *

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 (known as well-formed formulas when relating to formal language), each of which is an axiom, an assumption, or follows from the preceding sentences in the s ...

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

Dynamic and formal equivalence Dynamic equivalence and formal equivalence, in translation and semantics, are the principle approaches to translation, prioritizing respectively the meaning or the literal structure of the source text. The distinction was originally drawn ...

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 Informal education is a general term for education that can occur outside of a traditional lecture or school based learning systems. The term includes customized-learning based on individual student interests within a curriculum inside a regular c ...

, 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 countri ...

, 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