Active and passive voice are two modes of verb conjugation in French.
In the active voice, the subject of the sentence is the agent, or the one who performs the action. For example: "The cat eats the mouse." In this sentence, "the cat" is the subject (agent) who performs the action of eating the mouse.
In the passive voice, the subject of the sentence undergoes the action, or is the patient. To form the passive voice, we use the verb "être" (to be) followed by the past participle of the main verb, and the subject of the sentence is preceded by the preposition "par" (by). For example: "The mouse is eaten by the cat." In this sentence, "the mouse" is the subject (patient) that undergoes the action of being eaten by "the cat".
In summary, the active voice emphasizes the agent (the one who performs the action), while the passive voice emphasizes the patient (the one who undergoes the action).