A search engine is a Web-based software tool that enables users to locate content on the Internet. By periodically scanning the Internet's pages and by reviewing and listing directly submitted pages, each search engine compiles and maintains an index of Web sites. To initiate a search, the search engine user types in a keyword or phrase, and the engine then scans its database for Web sites that match the search criteria. The search engine uses its proprietary ranking algorithm to review the content and determine the relative relevance and ranking of each of the listed pages in relation to particular keywords.
Search engines along with Web directories are Web users' most important search tools. Therefore, Web sites that are not featured in search engine or Web directory indices will be seen by only a select few Internet users. The most common type of search engine is an algorithmic, spider- or crawler- based engine. A spider is a search engine element that scans (crawls) the Internet by following the hyperlinks that connect Web pages. The spider thus allows its search engine to compile and maintain its index. The search engine's proprietary algorithms then determine the importance and eventual ranking of the pages in the index.
