By “user,” I mean individuals like you and I as well as organizations. As far as you and I, as individuals are concerned, we have a laptop or a tablet, or a smartphone (or all of these) with some connection to the Internet (which is the “cloud”), and all we know is that when we need our email, it’s there, when we want to upload a video or share photos with family and friends, we can do it. We don’t care how Google or Facebook manage to store all this information that millions of users upload. That’s what is cloud computing to you and I - - to get access to our email, documents, Facebook, and Google+ etc. from any Internet-connected device, when we need it.
Now, if the user is an organization, they could, for example, go to Amazon Web Services and buy whatever computing services they need - - they can get database, storage, order fulfillment, payment service, or just plain computing platforms. That’s cloud computing to a corporation - - to be able to just go to the Amazon Web Services web site and order whatever type and amount of computing services they need. That’s what cloud computing is to organizations that need more computing than just the email, documents, etc. that we, as individuals need.
In summary, from the user’s point of view, it’s cloud computing if you can go to a vendor and buy whatever computing services you need and pay for just the amounts you use. All the technical definitions with jargon such as virtualization and elasticity are just technical explanations of how the cloud computing vendors do their magic, but that’s really not important to the users. What’s important to the users are: (1) a broadband connection to the Internet and (2) access their email, documents, etc from any device.
Interest in "cloud computing" over time:
Here are some interesting books related to cloud computing: