Foil

Foil may refer to:

Materials:
* Metal leaf, a thin sheet of metal
* Aluminium foil, a type of wrapping for food
* Plastic foil, a thin layer of plastics

Fluid Mechanics:
* Foil (fluid mechanics), a type of wing or blade used to provide lift
* Foil bearing, a type of fluid bearing

Paper making:
* Foil (papermaking), a type of ving under the wire in the wire section of a paper machine creating a vacuum pulse to eliminate water from the stock (fibre/water slurry).
* Ultrasonic foil (papermaking), a type of high frequency vibrating foil under the wire, creating cavitation, imploding vacuum bubbles, in the stock on the wire. The shock waves from the imploding bubbles will distribute the fibres more uniform in the paper web and this will give a stronger paper.

In aeronautics:
* Airfoil, used on aircraft
* Parafoil, a nonrigid airfoil, inflated during use

In arts and culture:
* Foil stamping, printmaking technique
* Foil (band), a Seattle grunge rock group c.1990-1998.
* Foil (literature), a character who emphasizes the traits of a main character
* Comedic foil, (or comic foil), is the straight man in a comedy team.
* Film Over Incandescent Light, an image projection technique

In mathematics:
* FOIL rule, a way to expand polynomials

In navigation:
* Hydrofoil, a type of boat using foils designed for water
* 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

Foil may also be:
* First Order Inductive Learner - a rule-based learning algorithm.
* FOIL programming language, one of two defunct computer programming languages
* Foil (fencing), one of the three weapons used in modern fencing