Wiktionary
n. An advertisement intended to change the public interest by raising awareness of an issue, affecting public attitudes and potentially stimulating action.
Wikipedia
A public service announcement (PSA) or public service ad, are messages in the public interest disseminated by the media without charge, with the objective of raising awareness, changing public attitudes and behavior towards a social issue. In the U.K, they are generally called public information films (PIFs); in Hong Kong, they are known as announcements in the public interest (APIs).
Public Service Announcement is the third studio album by Purling Hiss, released on October 12, 2010 by Woodsist.
Usage examples of "public service announcement".
Water bill, a public service announcement about Park Beautification Week, and a letter from Morocco.
Accept the phrase exactly for what it says and you have a public service announcement.
Free Public Service Announcement from Galactic Troopers Against Drunk Driving.
An old public service announcement illustrated how a basement room could be protected against modest fallout by taping cracks, blocking windows with books, and shoveling dirt shin-deep onto the floor above.