A foil is one of the three weapons used in the sport of fencing. It is a flexible sword of total length 110 cm (43 in) or under, rectangular in cross section, weighing under 500 g (18 oz), with a blunt tip. As with the épée, points are only scored by making contact with the tip. The foil is the most commonly used weapon in fencing.

Fencing is a combat sport that features sword fighting. The three disciplines of modern fencing are the foil, the épée, and the sabre ; each discipline uses a different kind of blade, which shares the same name, and employs its own rules. Most competitive fencers specialise in one discipline. The modern sport gained prominence near the end of the 19th century and is based on the traditional skill set of swordsmanship. The Italian school altered the historical European martial art of classical fencing, and the French school later refined that system. Scoring points in a fencing competition is done by making contact with an opponent.