What is the difference? While they are all commonly referred to as search engines, they are not all the same. Knowing the difference is important because it dictates the way in which you approach each in getting your site properly listed.
Directories like the Open Directory Project are human-edited lists of links broken down into a . . . well . . . directory. They present main categories on their home pages and then organize all the data under those headings, allowing the user to drill down further and further to the specific category that is relevant to their search. When you submit to directories, you begin by finding the appropriate category for your site and then suggest the site from that page. It is then reviewed by a real person (as opposed to being crawled by an electronic spider) and added or not.