Simple definitions
1. A Cloud is an organization of data stored on the Internet used to allow the user to save and move files easily, and Internet based storage software to easily allow files to be transferred over networks. Cloud storage can provide the benefits of greater accessibility and reliability; rapid deployment; strong protection for data backup, archival and disaster recovery purposes.
2. The Cloud is where the enterprise and storage service provider are separate and there aren't any cloud resources stored in the enterprise's data center. The cloud storage provider fully manages the enterprise's public cloud storage.
3. A Cloud is an easy accessible Internet-based storage device.
Expanded definition
The underlying concept of the Cloud dates back to the 1950s, when large-scale mainframe computers became available in academics and corporations, accessible via thin clients/terminal computers, often referred to as "static terminals," because they were used for communications but had no internal processing capacities. To make efficient use of costly mainframes, a practice evolved that allowed multiple users to share both the physical access to the computer from multiple terminals as well as to share the CPU time. This eliminated periods of inactivity on the mainframe and allowed for a greater return on the investment. The practice of sharing CPU time on a mainframe became known in the industry as time-sharing
The phrase also more commonly refers to network-based services, which appear to be provided by real server hardware, and are in fact served up by virtual hardware, simulated by software running on one or more real machines. Such virtual servers do not physically exist and can therefore be moved around and scaled up or down on the fly without affecting the end user, somewhat like a real cloud.
The Cloud is an image that indicates that the user doesn't need to know what goes on within the problem. A general name for