The dictionary definition of advertising is: "a form of persuasion that informs people about the goods and services they can purchase."
How is PR different to advertising?
Advertising is pretty different to PR. One keydifference is that you always give money for the space and time of an ad (or commercial, which is an insert which takes place on radio, television, or the Internet). On the other hand, editorial coverage made through PR s not paid for by the organization issuing the news release. The media pick this up and publish the story because they think it newsworthy and they gain through it, not as a paid for advertisement.
Another key difference is that, in advertising, you have almost full control over the content. Because you are giving money for advertising, the advertisement or commercial runs your precise content (called copy), as long as the copy complies with what is normally acceptable standards for advertising. In the instance of PR, the media outlet you are aiming for is under no duty to run the story in any format. If a media outlet wishes to run the story, an editor will normally rewrite the news release, or use relevant information from the release to create the news. (For instance, your public relations agency's news release might be used in a larger in your industry or profession.) Also you have no power over when the release or news will go ahead. All these choices are made by the editor of the media outlet
As you can observe, public relations is a cost-friendly way of getting your story out. Taking the time to write effective news releases and to construct a relationship with the pertinent media will, in time, pay dividends in exposure and prestige. Best of all, PR likely costs less than a one-off ad.