Meta search engines are search engines that search other search engines. Confused? To put it simply, a meta search engine submits your query to several other search engines and returns a summary of the results. Therefore, the search results you receive are an aggregate result of multiple searches.
While this strategy gives your search a broader scope than searching a single search engine, the results are not always better. This is because the meta search engine must use its own algorithm to choose the best results from multiple search engines. Often, the results returned by a meta search engine are not as relevant as those returned by a standard search engine.