Search engines help people find relevant information on the Internet. Major search engines have huge databases of web sites that surfers can search by typing in some text. Search engines send out spiders or robots, which follow links from web sites and index all pages they come across. Search engines decide the amount of weight that will be placed on various factors that influence results. Some want link popularity to be the most important criterion, while others prefer meta tags.
Search engines use a combination of factors to devise their formulas.
Directories - a whole different ball game Often confused with search engines, directories are completely different. Directories have rigid guidelines that sites must meet before being added to their index. Therefore, they have a smaller, but cleaner index. Factors that influence search engine rankings are irrelevant to directory rankings. Directories strive to categorize sites accurately and often correct categories suggested by a site's webmaster.