When ranking pages, search engines evaluate many different parameters and stick to certain rules known as ranking algorithms.
The two main questions search engines ask are:
- Is the content of the page relevant to the query?
- Is this particular page important to the query because other linked pages corroborate it.
On-page parameters include keyword frequency, prominence, and weight. Off-the-page factors include link popularity score, theme, and presence or absence of Open Directory [ODP] and Yahoo! listings.