The document discusses the passive voice in English grammar. There are two types of passive voice: active and passive. To change a sentence from active to passive voice, the object of the active sentence becomes the subject of the passive sentence, a form of the verb "to be" is used along with the past participle of the main verb, and the original subject becomes an optional prepositional phrase introduced with "by". Several examples are provided to illustrate how to transform sentences between active and passive voice.