SEO stands for "search engine optimization." It is the process of getting traffic from the "free," "organic," "editorial" or "natural" search results on search engines. All major search engines such as Google, Bing and Yahoo have primary search results, where web pages and other content such as videos or local listings are shown and ranked based on what the search engine considers most relevant to users.
I choose this website on search engine optimization to relate to Friedman's ninth flattener: In-forming. This resource explains how making your website popular through optimization influences the success of the web page.