How do you define a cloud?

A lot of us are bombarded with messages about the cloud and differening views and opinions on what is a cloud. I guess the National Institute of Standards and Technology  has weighed in on the topic to settle it once and for all.

Checkout their definition at : http://www.nist.gov/itl/cloud/upload/cloud-def-v15.pdf

You can also find more information about Symantec's view of the cloud at http://go.symantec.com/cloudavailability