The more technical and complex definition could be picked from wikipedia.org :P.
In concept, it is a paradigm shift whereby details are abstracted from the users who no longer need knowledge of, expertise in, or control over the technology infrastructure “in the cloud” that supports them. Cloud computing describes a new supplement, consumption and delivery model for IT services based on Internet, and it typically involves the provision of dynamically scalable and often virtualized resources as a service over the Internet
More simply, Cloud computing consists of hardware and software resources made available on the internet managed by Third Party Services. These services typically provide access to advanced software applications and high end networks of server computing. This enables availability of high end technology at economical prices.
2. Flexibility: User gets what he precisely requires. Available round the clock.
3. Hassle Free: Owned and managed by a third party.
Cloud can be either public or private. Public cloud is available to anyone on the internet. A private cloud is available to a limited number of people only. A public cloud used to create a private cloud is called virtual private cloud.
Cloud Computing can be divided into 3 Categories:
Infrastructure as a Service
Platform as a Service
You’ve might have actually used a Cloud Computing Service before. Some of the popular ones include:
Amazon EC2– Virtual IT
Google Apps – software as a service
Apple Mobile Me – Network Storage
Getting back to the 3 categories of Cloud Computing.
Infrastructure as a Service: The customers use the providers application program interface (API) to conifgure and manage their virtual servers. Since you pay for what you use, this is often referred as utilty computing. One of the examples is the Amazon Web Services, which provide virtual servers with unique IP addresses and blocks of stotrage.
Platform as a Service: If you’ve downloaded an app from the Apple App Store or used some Google Apps, you’ve used a product of this service. Devellopers create applications on the provider’s platforms. One way to do that is to use APIs. The app for the iPhone is build through the Software Development Kit (SDK) provided by Apple. Where the provider is Apple, and the interface -iPhone.
Software as a Service : A software hosted on a providers server is available for a stipulated time period. You pay for what you use. This cuts down the cost of large serves.
(This is intended to be just an introduction to “Cloud Computing”. )