The question is so simple but there are numerous answers to this. Well people often relate public relations with other professions. It is far beyond than any of the profession; it is the result of many economic reforms and political circumstances. So it has evolved into a very different entity in itself.
In the simplest way, talking about yourself is also Public relations. Enhancing, developing relationships, and finding ways to say is all about public relations.
Ordinary people tend to confuse Public Relations as advertising. Many associate it human resources while some think in terms of a receptionist on a company desk. The general perception is to link it with marketing.
I have tried to get a general opinion about Public Relations in this Video. Check it out!