If you've been trying figure out what "cloud computing" is, you're not alone -- and coming to the rescue is the National Institute of Standards and Technology. But as nice as the NIST folks are, they didn't have you in mind when they decided to put together an understandable definition of cloud computing.

Instead, the reason NIST decided to develop a definition is to provide technical guidance within the government and promote industry standards. To that end, computer scientists at NIST, in collaboration with industry and government, are producing a special publication that covers cloud architectures, economics, security, and deployment strategies. They point out, of course, that cloud computing is still evolving, adding that "its definitions, use cases, underlying technologies, issues, risks, and benefits will be refined in a spirited debate by the public and private sectors. These definitions, attributes, and characteristics will evolve and change over time."

So what is cloud computing, at least according to NIST?

Cloud computing is a pay-per-use model for enabling available, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, services) that can be rapidly provisioned and released with minimal management effort or service provider interaction. This cloud model promotes availability and is comprised of five key characteristics, three delivery models, and four deployment models.

Those five key characteristics are:

• On-demand self-service.
• Ubiquitous network access.
• Location-independent resource pooling.
• Rapid elasticity.
• Pay per use.

And the three delivery models?

• Cloud Software as a Service (SaaS).
• Cloud Platform as a Service (PaaS).
• Cloud Infrastructure as a Service (IaaS).

Cloud software takes full advantage of the cloud paradigm by being service oriented with a focus on statelessness, low coupling, modularity, and semantic interoperability

And finally, the deployment models:

• Private cloud.
• Community cloud.
• Public cloud.
• Hybrid cloud.

Each deployment model instance has one of two types: internal or external. Internal clouds reside within an organizations network security perimeter and external clouds reside outside the same perimeter.

Details on all of these characteristics and models are available here. Keep in mind that this document is only a draft, which means that if you have any thoughts, suggestions, complaints, or whatever, you can participate in the dialog. Just send email to cloud@nist.com.