What is the difference of passive and active voice in writing?

The active and passive voices are used to show what receives or initiates the action in a sentence.

With a passive voice, the subject receives the action: "The glass was knocked off the table."

In the active voice, the subject initiates the action: "I knocked the glass off the table."

The passive voice is often criticized as a way of de-emphasizing the actor, but it is useful, particularly if the actor is unknown, or you.