After couple googling wikipedia satisfied me with an actual and to-the-point definition,"Cloud computing is Internet ("cloud") based development and use of computer technology ("computing"). It is a style of computing in which dynamically scalable and often virtualised resources are provided as a service over the Internet.Users need not have knowledge of, expertise in, or control over the technology infrastructure "in the cloud" that supports them.
The concept incorporates infrastructure as a service (IaaS), platform as a service (PaaS) and software as a service (SaaS) as well as Web 2.0 and other recent (ca. 2007–2009) technology trends which have the common theme of reliance on the Internet for satisfying the computing needs of the users. Examples of SaaS vendors include Salesforce.com, NetSuite.com and Google Apps which provide common business applications online that are accessed from a web browser, while the software and data are stored on the servers.
The term cloud is used as a metaphor for the Internet, based on how the Internet is depicted in computer network diagrams, and is an abstraction for the complex infrastructure it conceals."
Ok I got the very basic idea; then I searched on youtube.com and this is what I though I should include :
Finally I'd like to add some of the cool cloud application that I I think really neat :