The threatened touch of another person with an intent to harm, without that person's consent.
Canadian tort law professor A. Linden in Canadian Tort Law, 6th Edition, (1997) defined it as:
".. the intentional creation of the apprehension of imminent harmful or offensive contact...
"An assault can be committed without a battery and battery can occur without an assault preceding it. For example, swinging at someone and missing is an assault but not a battery. Striking someone from behind, without his or her knowledge, is a battery but not an assault. Conduct which intentionally arouses apprehension of an imminent battery constitites an assault. Shaking a fist at another person, lunging at someone in an effort to attack and swinging an axe at another person are actionable assaults."
An overt act of the tortfeasor (or criminal defendant) which causes the plaintiff (or victim) to reasonably fear an imminent battery.
Eg. a cocked fist.
The common law limited assault to threats of imminent harm only; once cntact was made, the offence become battery.
Canada's Criminal Code (¶265) captures both the traditional concept of an assault and that of a battery:
"A person commits an assault when without the consent of another person, he applies force intentionally to that other person, directly or indirectly; he attempts or threatens, by an act or a gesture, to apply force to another person, if he has, or causes that other person to believe on reasonable grounds that he has, present ability to effect his purpose; or while openly wearing or carrying a weapon or an imitation thereof, he accosts or impedes another person or begs."