One of the two “voices” of verbs (see also active voice). A verb is in the passive voice when the subject of the sentence is acted on by the verb. For example, in “The ball was thrown by the pitcher,” the ball (the subject) receives the action of the verb, and was thrown is in the passive voice. The same sentence cast in the active voice would be, “The pitcher threw the ball.”
Note: It is usually preferable to use the active voice wherever possible, because it gives a sense of immediacy to the sentence.