Search Engine Optimization
Search Engine Optimization or SEO for short is a way to increase the number of visitors to a Web site by ranking high in the search results of a search engine such as Google, Yahoo, Ask, etc. The higher a Web site ranks in the results of a search, the higher up it appears in the search results. When your site ranks high, there is a greater chance that that site will be 
visited by a user. It is not common practice for Internet users to click through pages and pages of search results, so having your site rank high in a search is essential for directing more traffic toward the site.
SEO is an ongoing process and one that requires time and patience. There are many companies that specialize in providing SEO services; however, it is something that can be done on your own.
Below is a helpful video that explains what SEO is and how to improve your site's rankings on different search engines.
Search Engine Optimization SEO Tutorial by WebBizIdeas is for beginners.
It will cover SEO techniques that you can use TODAY that will increase your search engine rankings.
References:
Search Engine Optimization SEO Tutorial -- WebBizIdeas. Retrieved on June 9, 2009. http://www.youtube.com/watch?v=VBAJgksyhxo
SEO Image. Retrieved on June 15, 2009. http://www.northstudio.com/files/images/seo_0.jpg