The passive voice is a grammatical construction in which the subject of a sentence receives or undergoes an action, rather than performing it. In other words, the focus is on what happens to the subject (the receiver) rather than who does the action (the doer). The verb used in the passive voice is usually formed with the auxiliary verb "to be" followed by a past participle. For example: "The cake was eaten by John." In this sentence, the focus is on what happened to the cake rather than who did it.