Voice
In grammar, the voice 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 actor of the verb, the verb is said to be 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. (Wikipedia, Grammatical Voice)
"An active verb sresses the one doing it; a passive verb shifts the interest to what's being done, what it is, and also, at times, to what/whom it's being done to." (Gordon, The Deluxe Transitive Vampire)
Active voice: subject performs the action
Passive voice: action is performed upon the subject; contains a linking verb
Examples
Active: The cat was bitten by the dog.
Passive: The dog bit the cat.
Passive: The bonus checks were passed out by Mr. Cleaver.
Active: Mr. Cleaver passed out the bonus checks.