name

• (mnemonic) An acronym for the algorithm for multiplying two binomials.

verb

• (transitive) To apply the FOIL algorithm to.

noun

• (chiefly uncountable) Thin aluminium/aluminum (or, formerly, tin) used for wrapping food.
  "wrap the sandwich up in foil"
• (authorship, figuratively) In literature, theatre/theater, etc., a character who helps emphasize the traits of the main character and who usually acts as an opponent or antagonist, but can also serve as the sidekick of the protagonist.
  "Whereas the female invests heavily in the wake of conception, the male invests heavily prior to conception. Hitherto, the male has been regarded as the mere foil to the heavy investment in reproduction that renders the female the logjam (the limiting factor) in reproduction – reproduction overall is expandable by increasing the number of females, not by increasing the number of males."
• (figuratively) Anything that acts by contrast to emphasise the characteristics of something.
  "As she a black silk cap on him begun / To set, for foil of his milk-white to serve."
• (fencing) A very thin sword with a blunted (or foiled) tip
  "Blunt as the fencer's foils, which hit, but hurt not."

verb

• (transitive) To cover or wrap with foil.
• (nautical) Clipping of hydrofoil.