Advertising is the act of drawing the public’s attention to something, usually to sell it. Whatever is written on the sandwich board you're wearing is what you're advertising.
Advertising is getting the word out — whether it’s on a billboard, in a magazine ad, on a commercial, on the side of a blimp, or by singing it from the highest mountaintop. If you want to let people know about a product, service, or candidate, you run an advertising campaign. The word advertising may also be used for the advertisements themselves or the business of creating advertisements.