Foil can mean:

• In chemistry, a thin sheet of metal; see foil (chemistry).
• In fencing, a type of practice weapon; see foil (sword).
• In boating, a hydrofoil.
• In aeronautics, an airfoil is a type of wing or blade.
• Aluminium foil, a type of wrapping for food.
• In literature, a type of character; see foil (literature).
• In computer science, FOIL was the name of two old programming languages.