Search Engine Optimization is a marketing discipline focused on growing visibility in organic (non-paid, referred also as "natural" or "earned") search engine results. a matter of making sure your site is structured in a way that search engines understand, but it isn't just about building search engine-friendly websites, but also about making sites better for people too. Why SEO? The majority of web traffic is driven by the major commercial search engines, Google, Bing, and Yahoo!.