Web search tools can be divided into three categories: directories, search engines, and metasearch tools. In addition, many of these sites have other features, such as news feeds and shopping.
Directories list web sites by subject. Humans have looked at the sites and decided which ones are worth putting into the directory. Because of this human intervention, directories tend to search a smaller number of sites than search engines, but the sites they do search have already been assessed for content.
Search engines provide a searchable database of Web sites. There is no human intervention; computer programs gather information on new sites and adds them to the search engine's database. Search engine databases contain more sites than directories, but the sites have not been filtered by humans.
Metasearch tools do not maintain their own databases of Web sites; they run searches in other search tools. Using a metasearch tool is a good way to run many searches with a single search.
For more information about Web search tools, check the following sites:
