The voice in which the subject performs the action of the verb is called the active voice. In sentences using active voice, the subject of the sentence is the doer of the action. For example, in the sentence "The cat chased the mouse," the cat (the subject) is performing the action of chasing.
In contrast, the passive voice occurs when the subject receives the action of the verb. For instance, in the sentence "The mouse was chased by the cat," the mouse is not performing the action; instead, it is receiving the action of being chased.