The definition of assault in a criminal setting is putting someone under the reasonable beliefs that they are going to be imminently harmed by you or actually harm by you. For example, if that person is under the belief that you are about to strike them then that is an assault. If you do strike them, that then that is an assault, as well depending on the jurisdiction, some people use the eminent capacity under the word assault. Battery is actually when you inflict harm upon the person. Assault and battery depending on the jurisdiction are interchangeable terms so that is a general definition of assault.