Foil may refer to:

Materials

Foil (metal) A foil is a very thin sheet of metal, typically made by hammering or rolling.Britannica, The Editors of Encyclopaedia. "foil". Encyclopedia Britannica, 6 Nov. 2008https://www.britannica.com/technology/foil-metallurgy.Accessed 11 September 2022. Fo ...

, a quite thin sheet of metal, usually manufactured with a rolling mill machine *

Metal leaf A metal leaf, also called composition leaf or schlagmetal, is a thin foil used for gilding and other forms of decoration. Metal leaves can come in many different shades. Some metal leaves may look like gold leaf but do not contain any real gold. ...

, a very thin sheet of decorative metal *

Aluminium foil Aluminium foil (or aluminum foil in North American English; often informally called tin foil) is aluminium prepared in thin metal leaves with a thickness less than ; thinner gauges down to are also commonly used. Standard household foil is typ ...

, a type of wrapping for food *

Tin foil Tin foil, also spelled tinfoil, is a thin foil made of tin. Tin foil was superseded after World War II by cheaper and more durable aluminium foil, which is still referred to as "tin foil" in many regions (an example of a misnomer). History ...

, metal foil made of tin, the direct predecessor to aluminium foil *

Transparency (projection) A transparency, also known variously as a viewfoil, foil, or viewgraph, is a thin sheet of transparent flexible material, typically polyester (historically cellulose acetate), onto which figures can be drawn. These are then placed on an overhead ...

, a thin sheet of transparent flexible material, placed on an overhead projector for display to an audience

Fluid dynamics

Foil (fluid mechanics) A foil is a solid object with a shape such that when placed in a moving fluid at a suitable angle of attack the lift (force generated perpendicular to the fluid flow) is substantially larger than the drag (force generated parallel to the fluid fl ...

Airfoil An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or turbine. ...

, a foil operating in air **

Hydrofoil A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hydrofoil craft gains sp ...

, a foil operating in water ** Parafoil, a non-rigid airfoil, inflated during use *

Foil bearing A foil bearing, also known as a foil-air bearing, is a type of air bearing. A shaft is supported by a compliant, spring-loaded foil journal lining. Once the shaft is spinning fast enough, the working fluid (usually air) pushes the foil away from ...

, a type of fluid bearing

Arts and culture

Foil (architecture) A foil is an architectural device based on a symmetrical rendering of leaf shapes, defined by overlapping circles of the same diameter that produce a series of cusps to make a lobe. Typically, the number of cusps can be three (trefoil), four (qua ...

, decorative device derived from cusps of circles *

Foil stamping Hot stamping or foil stamping is a printing method of relief printing in which pre-dried ink or foils are transferred to a surface at high temperatures. The method has diversified since its rise to prominence in the 19th century to include a varie ...

, a printmaking technique *

Foil (fencing) A foil is one of the three weapons used in the sport of fencing, all of which are metal. It is flexible, rectangular in cross section, and weighs under a pound. As with the épée, points are only scored by contact with the tip, which, in electr ...

, one of the three weapons used in modern fencing *

Foil (fiction) In any narrative, a foil is a character who contrasts with another character; typically, a character who contrasts with the protagonist, in order to better highlight or differentiate certain qualities of the protagonist. A foil to the protagonis ...

, a subsidiary character who emphasizes the traits of a main character ** Comedic or comic foil, the straight man in a comedy

double act A double act (also known as a comedy duo) is a form of comedy originating in the British music hall tradition, and American vaudeville, in which two comedians perform together as a single act. Pairings are typically long-term, in some cases f ...

* "Foil" (song), "Weird Al" Yankovic's parody of Lorde's song "Royals"

Navigation

, 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 Bruce foil is a variant of the leeboard, consisting of a hydrofoil, foil typically mounted on an outrigger and always set at an angle to provide both lateral and vertical force. It was invented by Edmond Bruce in the early 1960s, and first publis ...

, a foil used on an outrigger to prevent a boat from heeling *

Centreboard A centreboard or centerboard (US) is a retractable hull appendage which pivots out of a slot in the hull of a sailboat, known as a ''centreboard trunk'' (UK) or ''centerboard case'' (US). The retractability allows the centreboard to be raised t ...

, a movable keel that functions as a foil *

Foilboard A foilboard or hydrofoil board is a surfboard with a hydrofoil that extends below the board into the water. This design causes the board to leave the surface of the water at various speeds. Background Laird Hamilton, a prominent figure in the inv ...

, a surfboard using a hydrofoil

Other uses

* People in a

police lineup A police lineup (in American English) or identity parade (in British English) is a process by which a crime victim or witness's putative identification of a suspect is confirmed to a level that can count as evidence (law), evidence at trial. T ...

* 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 The Forum of Indian Leftists (FOIL), or the Forum of Inquilabi Leftists, is a group of left-wing activists of Indian background. The organization describes itself as "a clearinghouse for radical Indian activists in the United States, Canada and Eng ...

, a political group of Indian intellectuals *

Freedom of information legislation Freedom of information laws allow access by the general public to data held by national governments and, where applicable, by state and local governments. The emergence of freedom of information legislation was a response to increasing dissatisfa ...

or Freedom of Information Law (FOIL) * Ultrasonic foil (papermaking), a type of high-frequency vibrating foil involved in papermaking *

Split tally A tally stick (or simply tally) was an ancient memory aid device used to record and document numbers, quantities and messages. Tally sticks first appear as animal bones carved with notches during the Upper Palaeolithic; a notable example is the ...

, in ancient financial accounting, the part of a split tally stick given to the recipient in a transaction {{Disambiguation