SEO stands for Search Engine Optimization. This is the process by which you can affect the position and visibility of your website in the unpaid section of a search engine's search results.
There are many ways to bring visitors and potential customers to your website. SEO is a powerful way to bring a visitors from search engines. Search engine visitors are highly targetted and very specific since they were actively searching for something.
You put in effort up front to prepare your website and it's content to be search engine optimized. Search engines crawl your website and rank your website among others on the Internet. Those websites that seem like they'll deliver the most helpful results to the searcher are ranked highest.