<p>&nbsp;Search engines are <strong>answer machines</strong>. When a person performs an online search, the search engine scours its corpus of billions of documents and does two things: first, it returns only those results that are relevant or useful to the searcher's query; second, it ranks those results according to the popularity of the websites serving the information. It is both <strong>relevance</strong> and <strong>popularity</strong> that the process of SEO is meant to influence.&nbsp;</p>