What is the difference between a directory and a search engine? Aren't they the same thing? The answer is no, but both are equally critical to achieving top rankings.
Search engines use computer programs known as "bots" or "spiders" to crawl the Internet looking for individual web pages to index into their databases. Each major search engine uses a complex set of algorithms and link popularity weighting to determine your page and site relevancy. Matching closely with the search engine's protocol can help you secure top ranking spots. Not aligning with the set protocols can result in low rankings or in some cases having pages removed from the search engine's database.
Directories operate somewhat differently. They usually involve human interaction with your site or pages. Known as an editor, this person will determine if your site meets the guidelines of their particular directory and also the category in which you want to reside. It is of utmost importance that your site be properly optimized for a directory prior to the submission process.
Improper directory optimization can cause a number of problems, including being placed in the wrong category. If the editor cannot easily determine the relevancy of your site by looking at the title and description, misplacement or even omission from the directory is likely.
A major online directory, such as Yahoo, can deliver boatloads of traffic. So it's important your site be optimized and categorized properly to take advantage of a potentially huge audience of users.