A meta-search engine is a search engine that sends user requests to several other search engines and/or databases and returns the results from each one. They allow users to enter their search criteria only one time and access several search engines simultaneously. Since it is hard to catalog the entire web, the idea is that by searching multiple search engines you are able to search more of the web in less time and do it with only one click. The ease of use and high probability of finding the desired page(s) make metasearch engines popular with those who are willing to weed through the lists of irrelevant 'matches'. Another use is to get at least some results when no result had been obtained with traditional search engines.

Metasearch engines create what is known as a virtual database. They do not compile a physical database or catalog the web. Instead, they take a user's request, pass it to several other heterogeneous databases and then compile the results in a homogeneous manner based on a specific algorithm.

No two metasearch engines are alike. Some only search the most popular search engines while others also search lesser-known engines, newsgroups and other databases. They also differ in how the results are presented and the quantity of engines that are used. Some will list results according to search engine or database. Others return results according to relevance, often concealing which search engine returned which results. This benefits the user by eliminating duplicate hits and grouping the most relevant ones at the top of the list.