The passive voice is a grammatical construction where the subject receives the action of the verb rather than performing it. It is formed using a form of the verb "to be" along with the past participle of the main verb. The object of an active sentence becomes the subject of the passive sentence. The passive voice is used when the performer of the action is unknown, unimportant, or obvious from context, and allows emphasis to be placed on the recipient of the action rather than on the performer.