Much more serious than a simple assault charge, assault with a deadly weapon (ADW) differs in a handful of ways.
The Law Behind Assault with a Deadly Weapon: Penal Code §245
A person must act with a deadly weapon in a way that would directly and probably result in the application of force to another person. As in simple assault, the act must be done willfully. Also as in simple assault, the act need not cause an actual injury. Only that the person doing the act was aware that it would cause a reasonable person to believe the act would probably result in the application of force.
The Present Ability to Apply Force
An example of this is a person swinging a baseball bat near another person in a menacing manner. If that person is close enough, and acts in a way that makes them aware that they can cause another person to basically be scared of an assault, the prosecution can show this to being equivalent to an assault with a deadly weapon (or “ADW).