The ranking of a website on a search engine results list that is due entirely to the search engine's algorithms evaluating the site rather than from a paid ad. The websites of companies that pay for ads are ranked either on the first page or very high in the results list. However, without paid ads, websites are ranked based on their popularity and the content of their pages, the latter often manipulated by optimization specialists who try to trick the search engine (see page ranking and search engine optimization). Also called a "natural search." See vertical search engine and search engine.