The basic types of search engines include: Web crawlers, meta, directories and hybrids. Within these basic types, there are many different methods used to retrieve information. Some common search engines include Google, Bing and Yahoo.
Crawlers, or spiders, are the most common type of search engine. Crawlers are user friendly and produce a large number of results. These can be manipulated with search engine optimization, a ranking system used to organize search results. Filtering through the huge number of search results can be difficult for inexperienced users looking for specific information. Examples of crawlers are Google and Bing.
Meta engines search multiple search engines at the same time to get a composite list, and includes engines like Dogpile. Directories are run by humans instead of bots and programs. Human editors review each page or item submitted to be included to ensure that the results are relevant and high quality. Examples of directories include Open Directory Project and LookSmart. Hybrids are a combination of crawlers and directories that either give you a choice between the two result groups or mix the groups together. Some hybrids include Yahoo Directories and MSN Search.
Within these groups, there are numerous search engines and often these engines have a specialty. For example, there are search engines that focus on searching for educational results that return intellectual articles, such as Google Scholar.