Search engine optimization (SEO) is the process of improving the volume or quality of
traffic to a web site from search engines via "natural" or un-paid ("organic" or
"algorithmic") search results as opposed to search engine marketing (SEM) which deals
with paid inclusion. Typically, the earlier (or higher) a site appears in the search
results list, the more visitors it will receive from the search engine.
WIKI Article on SEO, February 21, 2010