Simon Wardley of Canonical provides a lively discussion of the definition of Cloud Computing. Having criticised the profusion of Cloud definitions he then produces his own – and one which I particularly like:

“Cloud Computing is a generic term used to describe the disruptive transformation in IT towards a service based economy driven by a set of economic, cultural and technological transformations”

See the video of his talk on YouTube: YouTube – OSCON 09: Simon Wardley, “Cloud Computing – Why IT Matters”.