Public Relations
Public Relations is the name for all of the efforts that allow you to reach the public without a paid endorsement.
It is all of your efforts to generate goodwill towards your company.
Public Relations Activities
Got something to be proud of? Publicize it. Do your employees do great things? Publicize it. Did you win a new account? Publicize it. You get the idea. You can get articles written about you, publish articles yourself, become known as an expert. You can give speeches, attend trade shows, hold seminars. These all come under the umbrella of good PR.
Corporate Identity
Public Relations also covers your corporate identity. Along with the products and services that you market, your company has it's own brand. A great product from a company with a bad reputation can sell less than a bad product from a company with a great reputation.