When a user conducts a search using Google, Yahoo, or virtually any other search engine (Technorati, Blogrolls, etc…) they are presented with a list of pages that are deemed relevant to that search. Typically a page is considered relevant if it contains a number of instances of the word or term that the user searched for.

Furthermore the pages are then ranked according to how relevant and how much authority they are perceived to have. Considering results are usually returned in a second or so, there’s a lot of calculations that need to be conducted to ensure that users get the best information quickly.

Page relevance, or on page SEO, looks at the existence of keywords in the page content. While it was once considered standard practice to aim for a specific number of keyword instances in a page, search engines now encourage more organic results and so the number of keywords can be considerably more flexible.

Search engines are also believed to look at factors like domains and some HTML tags in order to determine the value of a page.

Off page optimization concentrates specifically on the number and value of links that direct to each of the pages. Each link is considered individually and if it uses a specific keyword or a related keyword then it indicates that the resulting page is relevant to that term.

Another factor considered in calculating a page’s rank is the authority that it is perceived to have. Links from pages with more authority will be given greater weight than those from sites with less authority.