An organic search result is a listing generated by a search engine's "organic process." The organic results are displayed in the main body of the search engine results page in contrast to advertisements or paid inclusion results. Because outcome from organic listings will not cost you any money and your site will be ranked organically, the amount of time and effort it requires for you to write content for specific keywords varies. You can select which pages to optimize and how much time, compared to writing a PPC ad.