Organic or Natural Search
Most of the search engines offer two types of results to their customers: Results by payment (Normally located at the top or the side of the page) and organic or natural results. The payment results will make your website to be located in a good position, even though most of the customers consider this as advertising, and generally they will avoid those sites, considering the organic results as a better option.
Most of the people consider that organic or natural results are a more precise reflect of what they are looking for, as they are generated by popularity and common sense. in SEO, we will try to adjust the content of your webpages to get a good result in the organic search.