Search engines are huge databases of submitted websites that rely heavily on automated systems to both catalogue and rank web pages, directories use real people (gasp!) to catalogue and arrange submitted websites into their databases and hybrid search engines are associated directories maintained by search engines, humanly edited and generally difficult to get on to.

Search engines use a software 'spider' or 'crawler', and this little fella spends its time roaming cyberspace reading every site it finds, and then following links to other pages within the site. Everything the spider finds goes into the search engine's index, although this can sometimes take several weeks.

Spiders regularly return to sites, usually every month or two, to look for changes, sending the information back to the search engine index. For this reason it's important to keep your meta information up to date to reflect any changes on your site.

The really clever stuff is done by the search engine software. This sifts through the millions of pages recorded in the index to find matches to a search and then rank them in order of what it believes to be the most relevant. This is calculated by its own unique criteria which can involve page titles, keywords, descriptions, page text and link popularity