The Bonsai Framework concept of Cloud Density is to reduce the philosophy of reducing Cloud cost using a combination of isolation technology and or techniques like using zero footprint and multiple instances.
Some examples of enabling isolation technology are Container (FreeBSD Jails, LXC, Docker, Garden) and platforms (Cloud Foundry, Apache Mesos).
In best practice, the output of Cloud Density should be savings by reducing the number of Cloud virtual machines while maintaining close to equivalent reduced cost due to less Cloud virtual machines. At the same time, the system should match the service level of a standard larger cloudscloud.