There is no shortage of predictions regarding the future of data center power densities, but their track-record over the last decade has been poor. At the same time, there is also a general inconsistency in the way different groups define and discuss the topic of the high-density data center. This paper will touch on these predictions and definitions. Following that, it will tie the density discussion into the other main data center goals: efficiency, capacity planning, and uptime. Finally, it will provide a bit of guidance for cutting through the fog where it comes to how power and equipment densities vary within a data center and for planning how to handle the varying densities at the data center rack.