Announcement on television or radio serving the public interest and run by the media at no charge. For example, a utility company might do a series of PSA's on the subject of saving energy in the home. Each one would feature the company's name.
Announcements that inform the public about safety and health information, community services or public affairs. Produced and programmed much like commercials, but usually not produced for profit.
An advertisement or commercial that is carried by an advertising vehicle at no cost as a public service to its readers, viewers, or listeners. While the no cost aspect is appealing, a library or other agency utilizing this media quickly realizes there is no control on the most effective time of placement.