The voice of a verb may be defined as that form of the verb which shows whether the subject is the doer of the action of the verb or the action of the verb happens to the subject.
Compare the following two sentences:
The old man caught the thief.
The thief was caught by the old man.
Active voice- When the subject of s verb is the doer of the action of the verb, the verb is in the active voice.hence,the 1st sentence is in active voice.
Passive voice- When the action of a verb happens to its subject, and it is denoted by the reciever of the action, the verb is in the passive voice.