Updated 06Nov2014: I've updated my thoughts on the layers to take into account both things I learned since this was originally written. OpenStack is, as it name implies, a stack of services to provide "components for a cloud infrastructure solution". [1] There are layers of services, some interdependent on each other, some only dependent on the layers below it. For some time there has been a PC dance around 'labelling' projects that may or may not be at a layer that it wants to be in. Back in the day, the term 'core' was thrown around to identify the services