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). They may refer to:

Dress code and events

* Formal wear, attire for formal events * Semi-formal attire, attire for semi-formal events * Informal attire, 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, 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, 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