UNIT 1:

Passive voice
one can change the normal word order of many active sentences (those with a direct object) so that the subject is no longer active, but is, instead, being acted upon by the verb - or passive.

Passive voice is the one that changes the normal Word order to make it no longer active. Passive voice is when the subject is the focus.

Active voice
In most English sentences with an action verb, the subject performs the action denoted by the verb.
 
With the active voice the subject, the doer of the action, is in focus.