Cloud is a system where users acquire and manage technology resources on their own while the owners of those resources still maintain control of them.
Whether you like mine or not, I think these two definitions offer nice book-ends: NIST’s is technical, and mine is conceptual.
But neither is practical, though NIST gets closer than I do. What I mean by this is that, if you want to try to figure out whether cloud is the right model for a particular purpose, you need a definition of cloud that you can apply to that purpose to show the costs and benefits in measurable ways. Conceptual definitions won’t do that at all.
NIST’s technical definition of cloud has the right components. But it also has too many options listed. So I suggest cutting it down to the essential characteristics of cloud:
- On-demand (available in an automated fashion; no posted closing hours)
- Self-service (by human or machine)
- Charged or shown back
If you have all four, you have cloud. They form a nice pair of couples. The first two are the technical benefit of cloud: resource use driven directly by the user. And the last two are the technical counterweights required to keep cloud manageable: seeing what users are doing, and enabling accountability.
Next, what I left out.