1. A system comprising: at least one processing unit; and at least one computer-readable storage media storing instructions which, when executed by the at least one processing unit, cause the at least one processing unit to: store a plurality of communications, the plurality of communications including a subset of individual communications that mention a common hashtag and other communications that do not mention the common hashtag, wherein the common hashtag begins with a “#” symbol in each individual communication of the subset; filter the plurality of communications to identify the common hashtag referenced in each individual communication of the subset; compute scores reflecting semantic relationships between the individual communications of the subset that mention the common hashtag; select one or more of the individual communications of the subset that mention the common hashtag based on the scores; and generate a summary of the common hashtag, the summary representing the one or more selected individual communications of the subset that mention the common hashtag.