A website that maintains an index and short summaries of billions of pages on the Web, Google being the world's largest. Most search engine sites are free and paid for by ads. Yahoo was the first search engine to gain worldwide attention, and it initially indexed most of its content manually, creating a hierarchical directory that was put together by human observation. It was known then as a "directory" rather than a "search engine." However, as Web content grew exponentially, it became impossible to index everything manually. Web Spiders Most indexing is done automatically by Web "spiders," which are programs that "crawl" the Web around the clock looking for all the pages they can find. By following the links from one page to another, they scour billions of pages and summarize them in massive databases, which is what you query when you do a search. Metasearching "Metasearch" engines search other search engines and bring you results as if you went to each of them independently (see below). The Deep Web An enormous amount of content that websites offer resides in databases that are not exposed to the search engines like ordinary HTML pages with links to each other. This "deep Web," which is thousands of times larger than the public Web is accessible from the site itself and may require membership or a paid subscription. The Portal Many search engine sites evolved into a portal. Instead of offering content only from other websites, they have their own content and features such as free e-mail, chat rooms and shopping. For information about all major search engines, visit www.searchenginewatch.com. See portal, Web white pages, Web yellow pages and information broker.