The passive voice is a grammatical construction where the subject receives the action rather than performs it. In the passive, the doer or subject of the action is either unknown or unimportant. Some key characteristics of the passive voice are that it uses forms of the verb "to be" along with the past participle of the main verb, and it often omits the agent or doer of the action. The passive voice is commonly used when the agent is unknown or unimportant to the topic being discussed.