Formal

Formal and Informal, and Formality and Informality, may refer to

• Form (disambiguation)
• Formalism (disambiguation)

Dress code and events

• Formal wear, required attire for 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, 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, 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
• Formal derivative, 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
• 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, nickname for:
  • Formaldehyde
  • Dimethoxymethane, a chemical derived from formaldehyde

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, 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