Meta search offered by a number of specialized search engines, such as Dogpile, MetaCrawler, Mamma.com, ixquick, ProFusion, and Kart00 is the concept of simultaneously engaging multiple search engines and have each of the source engines return its own list of results for a given search phrase, thus, theoretically, providing more comprehensive results than regular Web searches.
Most meta-search engines display the combined search results on one, prioritized list, which might mix listings from several sources. Other meta-search engines present each source search engine's search results separately, so that the user not only can tell exactly which results each individual engine returned, but also how each one ranked the results. There is no guarantee that meta-search results are more comprehensive than those of regular search engines, but because more sources will be queried there is at least a chance that utilizing a meta-search engine will provide results that a regular, single-engine search engine would have missed.
Because they usually rely on their partners to generate the search results, most meta search engines do not maintain their own indices of Web content. To be featured in a meta search engine's results, Web pages should be listed in the index/indices of the engine(s) the meta search engine employs when generating search results.
