title: Foil
text: # Foil
  
  Foil may refer to:
  
  ## Materials
  
  * Foil (metal), a quite thin sheet of metal, usually manufactured with a rolling mill machine
  * Metal leaf, a very thin sheet of decorative metal
  * Aluminium foil, a type of wrapping for food
  * Tin foil, metal foil made of tin, the direct predecessor to aluminium foil
  * Transparency (projection), a thin sheet of transparent flexible material, placed on an overhead projector for display to an audience
  
  ## Fluid dynamics
  
  * Foil (fluid mechanics)
     * Airfoil, a foil operating in air
     * Hydrofoil, a foil operating in water
     * Parafoil, a non-rigid airfoil, inflated during use
  * Foil bearing, a type of fluid bearing
  
  ## Arts and culture
  
  * Foil (architecture), decorative device derived from cusps of circles
  * Foil stamping, a printmaking technique
  * Foil (fencing), one of the three weapons used in modern fencing
  * Foil (fiction), a subsidiary character who emphasizes the traits of a main character
     * Comedic or comic foil, the straight man in a comedy double act
  * "Foil" (song), "Weird Al" Yankovic's parody of Lorde's song "Royals"
  
  ## Navigation
  
  * Hydrofoil, a type of high-powered motorboat that uses underwater foils to lift its hull above the water when moving at high speeds
  * Bruce foil, a foil used on an outrigger to prevent a boat from heeling
  * Centreboard, a movable keel that functions as a foil
  * Foilboard, a surfboard using a hydrofoil
  
  ## Other uses
  
  * People in a police lineup
  * First-order inductive learner – a rule-based learning algorithm
  * The FOIL method, a mnemonic in algebra, to expand the product of two first-degree polynomials ("linear factors")
  * FOIL (programming language), either of two now-defunct computer programming languages
  * Forum of Indian Leftists, a political group of Indian intellectuals
  * Freedom of information legislation or Freedom of Information Law (FOIL)
  * Ultrasonic foil (papermaking), a type of high-frequency vibrating foil involved in papermaking
  * Split tally, in ancient financial accounting, the part of a split tally stick given to the recipient in a transaction
  