Search engines and directories seem like they’re the same thing. Not quite. Both services have things that are similar, and things that are different. A whole lexicon of specialized terminology exists to try and describe them. If you’re new to the web, sometimes it’s helpful to have a translator.

Internet services like Google, Yahoo!, Microsoft’s Live Search, Alta Vista, Lycos, Open Directory, and others, are all considered to be search engines. Along with these services there are also Internet information portals, online services, Internet guides and Web Directories. Each one has a slightly different set of features and services. All of it is designed to help you find websites.

Most of the time when we talk about "search engines," "web directories," and "informational portals" we’re talking about services like Google, Yahoo!, and the like. If you want to get specific, though, there are differences between them. Strictly speaking, they are different things.

For example, Open Directory (a.k.a. dmoz.org) is a web directory, not a search engine. The key difference, here, is that search engines use "spider" programs to "crawl" across the web. The spider programs are what actually retrieves the information about a given website and brings it back to the search engine to install that site in the search engines databases. Directories, on the other hand, are built by humans. They’re hand-assembled databases. In a web directory, humans determine what to list, and how to list it, not a spider program. Google, Yahoo!, Alta Vista, Live Search, Excite, HotBot, Infoseek, Lycos and good old WebCrawler are actual search engines. Many of the others are actually directories.

Both search engines and directories offer the same basic Internet search features. How they are implemented, and what additional services they have available, allow individual search engines to differentiate themselves. This is how they differentiate themselves, appeal to a specific audience and competing with the rest. They create different "value-added" services.

All of these services are made available for free to the end user. Most often, search engines make their money by selling advertising space within their sites for other websites – just like yours.

When you visit Yahoo.com, for example, you’ll see a free internet search service near the top of the page. For Yahoo!, it doesn’t end there. The also have categories you can browse, features sites and stories you can peruse, online photo collections, ads for other websites, and even free online email services. They even have a list of the top searches of the day.

There’s so much stuff here, it’s easy to get distracted. Sometimes, services like Yahoo! are referred to as Internet Portals. They serve as entry points to start your explorations on the web.

When you do a search, a search engines matches up what you typed into the search box (what you typed is called a "keyword.") with the content of all the websites they have listed in their insanely huge databases. The spider programs have already looked through the site and created an "index" of the things they found on the site. The search engine compares your search words with the search engine’s index, and returns links to websites it things are related to whatever you typed in. Directories do this too. The difference is that the index was created by human beings, not spider programs.

Clear as mud?