Sentence:  A verb is typically described as active when its subject is the <WSD>agent</WSD> or actor. By contrast, a verb is said to be passive when the subject does not perform the action, but is the patient, target, or undergoer of the action. 
Meaning of the word marked with <WSD> tags:  (grammar) The participant of a situation that carries out the action in this situation, e.g. "the boy" in the sentences "The boy kicked the ball" and "The ball was kicked by the boy".