16. The computer-readable storage medium of claim 15 , wherein the trending score is also based on a popularity score, wherein the popularity score includes a measure of social activity associated with one or more pieces of content each of which reference the topic.
16. The computer-readable storage medium of claim 15 , wherein the trending score is also based on a popularity score, wherein the popularity score includes a measure of social activity associated with one or more pieces of content each of which reference the topic. 19. The computer-readable storage medium of claim 16 , wherein calculating the trending score further includes ranking topics based on the velocity of each topic and the popularity score of each topic and calculating the relevance of each of the plurality of candidate pieces of content based on the ranked topics.