Earlier this week, the National Institute of Standards and Technology (NIST) published a formal definition for cloud computing, two years after the first draft was proposed. Despite an abundance of primers on the subject, the answer to the “What is cloud?” question remains somewhat murky, so a formal pronouncement from an established standards body such as NIST should be well-received by a community that is largely still seeking clarity on the “cloud” issue.

So without further ado, here is NIST’s formal definition:

“Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.”

NIST explains that the “definition is intended to serve as a means for broad comparisons of cloud services and deployment strategies, and to provide a baseline for discussion from what is cloud computing to how to best use cloud computing.”

More fine-grained examples will of course take into account user-specific requirements. For example, the decriptor “convenient” is a relative term with a range of interpretations that depend on the user, application, and industry. One person’s “convenient” is another’s “latency issue.”

The NIST definition goes on to list five characteristics considered essential to cloud computing: on-demand self-service, broad network access, resource pooling, rapid elasticity or expansion, and measured service. There are also three “service models” (software, platform and infrastructure), and four “deployment models” (private, community, public and hybrid) – which combine to describe a delivery mechanism. These elements are further clarified in “The NIST Definition of Cloud Computing” (SP800-145.pdf).

Although just recently finalized, the NIST definition has long been the working standard for the community. In fact, the same version served as the US contribution to the InterNational Committee for Information Technology Standards (INCITS), the group that is working to develop a standard cloud computing definition at the international level.