This is a question that we discuss quite often at Edentity.  It’s one of those things, kind of like “web services” where the terminology has been thrown around by a ton of people and means a lot of different things.

Here’s my favorite diagram so far, which is a visual breakdown of the material presented here by NIST, visualized by the folks at Cloud Security Alliance.

What I like about this diagram is that is shows several different ways that we can differentiate our definitions of cloud computing, from the essential characteristics, or which “Broad Network Access" and “On-Demand Self-Service” (which often are used on their own to define cloud computing) are but a couple of things that help make something “cloud”.

The most important section from my point of view is the middle one – the Service Models.  This represents the different ways that cloud computing can be exposed from the ground up.  It can be an Infrastructure, a Platform or a piece of Software that an end user interacts with.

This is the future, folks.

more later- joel

Read the complete post at http://weblogs.asp.net/joelvarty/archive/2010/03/16/what-is-cloud-computing.aspx