Passive and Active Voice

There are two special forms for verbs called voice:

Active voice
Passive voice

The active voice is the "normal" voice. This is the voice that we use most of the time. You are probably already familiar with the active voice. In the active voice, the object receives the action of the verb:

active: subject - verb - object
>
Ex: "Cats eat fish."

The passive voice is less usual. In the passive voice, the subject receives the action of the verb:

passive: subject - verb - object
<
Ex: "Fish are eaten by cats."

The object of the active verb becomes the subject of the passive verb:

subject - verb - object
Active: "Everybody drinks water."
Passive: "Water is drunk by everybody."


http://www.englishclub.com/grammar/verbs-voice.htm

GRAMMAR - 'Voice':

In grammar, the voice (also called diathesis) of a verb describes the relationship between the action (or state) that the verb expresses and the participants identified by its arguments (subject, object, etc.).

> When the subject is the agent or doer of the action, the verb is in the active voice.
> When the subject is the patient, target or undergoer of the action, it is said to be in the passive voice.