Not all search engines have bots crawling the web for the latest content. Some of them are actually set up by humans who review every website submitted. A real person decides if the website should be included, and if so they write a 25 word summary and place it in the appropriate category of their "Directory."
Users are then able to search the directory using word phrases, but also you can select categories and sub categories until you find what you are looking for. In other words, you can look through a directory just like you would look through your local yellow pages phone book, if you still have one that hasn't been immediately recycled.