Found : History of PSYOP
Psychological operations may be defined broadly as the planned use of communications to influence human attitudes and behavior … to create in target groups behavior, emotions, and attitudes that support the attainment of national objectives. The form of communication can be as simple as spreading information covertly by word of mouth or through any means of multimedia.
A psychological warfare campaign is a war of the mind. Your primary weapons are sight and sound. PSYOP can be disseminated by face-to-face communication, audio visual means (television), audio media (radio or loudspeaker), visual media (leaflets, newspapers, books, magazines and/or posters). The weapon is not how its sent, but the message it carries and how that message affects the recipient.