Rather than read the content of your pages like a search engine does, directories ask for specific information about the site and require that you select an appropriate category. At that point, a human editor reviews your site based on your request and decides whether to include you in the directory and if so, where to include you. If you make any significant changes to your site, be sure to update your directory registration. Search engines operate much in the same way as your local librarian would if you were to come in and ask for a book on Great Lakes shipping, for instance. The librarian would start with books that contain those words in the title.
Frequency is another factor search engines look for.
A search engine will look for how many times the keywords appear on your page. The more times the words appear, the more relevant the site is thought to be. There are other tips, tricks and methods to make your page rank higher in searches and thus make it easier for potential customers to find you in the ever-expanding world of the Internet.