SEM

Search Engine Marketing or SEM is a form of internet marketing which it allows the visibility of your websites to the page result pages of the search engine by means of five ways: paid placement, contextual advertising, digital asset optimization, paid inclusion, and the most popular, search engine optimization (SEO)
Search engine optimization is very powerful just for your website to be in the links to be viewed in search engine results page. Click this link for more information about SEO.
http://shifthappens-tholitz.blogspot.com/2010/01/seo.html