A human search engine is a search engine that uses human participation to the search results and assist users in clarifying their search request. The goal is to provide users with a limited number of relevant results, as opposed to traditional search engines that often return a large number of results that may or may not be relevant.
Examples of human search engines include ApexKB, ChaCha, Mahalo.com and the now defunct NowNow (from Amazon.com) and Sproose.