Copywriting is a form of business writing that's designed to persuade others to act, make a decision, or see your point of view. That would include any advertising, direct mail, sales letters, web sites, press releases, brochures, annual reports, professional resumes or bios, speeches, and about a million other things that haven't even been dreamed of yet. If you think about it, everywhere you look, from magazines to the sides of buses to the mail in your mailbox, someone had to write that. Why couldn't it be you?
Advertising agencies often hire full-time copywriting staff, which is a great opportunity to get your foot in the door. Or, if you're more entrepreneurial, try your hand at freelance copywriting. There's lots of work to be had out there, and many people are willing to spend money for a seasoned, knowledgeable writer. Freelance copywriting benefits you because you make your own schedule and charge your own rates, but it also benefits the client, because they no longer need to pay a full-time employee a salary and benefits. It's a win-win.
A little background in marketing or journalism is a good idea for getting started in copywriting. But those persuasive skills are easily learned with a few classes and some on-the-job experience. And the best part is that you're doing what you love, and what you're great at, while getting paid to do it.