What is a Cloud?

There's been a load of debate over Cloud and what it is... Thanks to Pete Peterson of Wells Fargo Bank for providing this useful extract and link to the NIST source

This NIST definition is the most concise and "share"able definition I've read. My favorite so far. Clip included:

"Cloud computing is a model for enabling 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. This cloud model promotes availability and is composed of five essential characteristics, three service models, and four deployment models."
- NIST Definition of Cloud Computing

Whilst virtualization technology is an obvious aid to 'Cloud' computing. It's probably worth saying that virtualization is not The Cloud - to the users I speak to it's clearly a way of describing computing as a utility or outsourced service delivery; which includes pretty much all the traditional managed services, some new ones and layered under SaaS, IaaS and PaaS.