The term Search Engine has become a catch-all phrase for all kinds of search services. Without these free resources it would be much more difficult to find anything anywhere on the 'Net. Searching is fundamental to gathering information on the Internet. Each service has their own way of compiling and collecting information. One way to think of the differences between these two kinds of engines is to think of web sites as books.
Indexes regularly scan the Internet for Web pages and record the HTML content and key words.
They also have the ability to follow any links associated with scanned pages and get even more information. The advantages of this kind of service is their data bases are very large and updated often by spiders working around the clock. They catalog Web pages in a computational manner without human intervention. A search engine's spider catalogs all the pages of a given web site, listing for you only the pages that match the words or phrases you're searching for. A drawback to using services of this type is that sifting through so many hits to find what you're looking for is sometimes a daunting task.