The term Search Engine Optimization describes a diverse set of activities that you can perform to increase the number of desirable visitors who come to your website via search engines (you may also have heard these activities called Search Engine Marketing or Search Marketing). This includes things you do to your site itself, such as making changes to your text and HTML code. It also includes communicating directly with the search engines, or pursuing other sources of traffic by making requests for listings or links. Tracking, research, and competitive review are also part of the SEO package.
SEO is not advertising, although it may include an advertising component. It is not public relations (PR), although it includes communication tasks similar to PR. As a continually evolving area of online marketing, SEO may sound complicated, but it is very simple in its fundamental goal: gaining targeted visitors.