1. One or more computer-readable storage media having computer-executable instructions embodied thereon that when executed by a computing device perform a method of adding terms from a related document to a document description for a target document, the method comprising: determining that a term found in the related document does not match a filter criteria, wherein terms that match the filter criteria are not added to a document description for the target document, wherein the document description for the target document comprises terms within a plurality of signal streams that are associated with the target document; calculating a similarity score for the term, wherein the similarity score is based on cosine similarity between the target document and the related document; calculating a source-credibility score for the term based on a static rank of the related document, wherein the static rank is based on an independent popularity score for the related document; calculating a corroboration score for the term based on similarity between terms used in links and the term; calculating a uniqueness score for the term based on whether the term is currently associated with the document description through other sources; calculating a term score for the term based on the similarity score, the source-credibility score, the corroboration score, and the uniqueness score; and associating the term with the document description because the term score is above a threshold score.