What is the definition of fencing?

In the broadest possible sense, fencing is the art of armed combat involving cutting, stabbing, or bludgeoning weapons directly manipulated by hand, rather than shot, thrown or positioned. Examples include swords, knives, pikes, bayonets, batons, clubs, and similar weapons. This definition is a stretch of the word, however. "Fencing" wasn't invented until either the Renaissance or at the very end of the Late Middle Ages, depending on who you ask. For weapon styles pre-dating this origin, "melee" or "Western Martial Arts" are better descriptors. In contemporary common usage, "fencing" tends to refer specifically to European schools of swordsmanship and to the modern Olympic sport that has evolved out of them.

Fencing is one of the four sports which has been featured at every modern Olympic Games. Currently, three types of weapon are used in Olympic fencing:

Foil — a light thrusting weapon; the valid target is restricted to the torso; double hits are not allowed (see priority rules below).
Épée — a heavy thrusting weapon; the valid target area covers the entire body; double hits are allowed.
Sabre — a light cutting and thrusting weapon; the valid target area includes almost everything above the waist (excluding the back of the head and the hands); double hits are not allowed (see priority rules below).