17. A non-transitory computer-readable storage medium that stores instructions which, when executed by one or more processors, cause the one or more processors to perform steps comprising: receiving an original question from a user; generating two or more queries based on the original question; submitting each of the two or more queries to a search engine; for each particular query of the two or more queries, receiving, from the search engine, a separate search engine result for that particular query, thereby receiving a plurality of search engine results; wherein the search engine result for each particular query corresponds to a separate document set; wherein the plurality of search engine results correspond to a plurality of document sets; generating a single concept set based on term in documents from the plurality of search engine results; wherein the single concept set is generated by, for each search engine result in the plurality of search engine results, identifying terms in documents from the search engine results, and adding at least a subset of said terms to said single concept set; using the single concept set to determine how to respond to the original question by performing at least one of: generating a refined set of search results for the original question based on the single concept set, and returning the refined set of search results as a response to the original question; or using the single concept set to identify questions similar to the original question; wherein the steps are performed by one or more computing devices.
27. The non-transitory computer-readable storage medium of claim 17 , wherein the step of identifying terms in documents from the search engine results comprises mapping particular terms in a particular document within the particular document set to Wikipedia entries that correspond to the particular terms; and wherein the step of adding said terms to said concept set comprises adding, to said concept set, particular terms that are primary topics of at least some of said Wikipedia entries.