Most people incorrectly believe that search engines and directories are the same.
A search engine has two parts, a spider and an indexer. The spider is the program that fetches the documents, and the indexer reads the documents and creates a catalog or database based on the words or ideas contained in each document. The main difference between a search engine and a directory is that a directory does not make use of a spider or robot. In other words, a directory will not list your web page if you do not register it with them. Directories are usually divided into categories and you must submit your URL under the most appropriate categories.