Cloud computing is a term used to refer to a model of network computing where a program or application runs on a connected server or servers rather than on a local computing device such as a PC, tablet or smartphone. Like the traditional client-server model or older mainframe computing, a user connects with a server to perform a task. The difference with cloud computing is that the computing process may run on one or many connected computers at the same time, utilizing the concept of virtualization. With virtualization, one or more physical servers can be configured and partitioned into multiple independent "virtual" servers, all functioning independently and appearing to the user to be a single physical device. Such virtual servers are in essence disassociated from their physical server, and with this added flexibility, they can be moved around and scaled up or down on the fly without affecting the end user. The computing resources have become "granular", which provides end user and operator benefits including on-demand self-service, broad access across multiple devices, resource pooling, rapid elasticity and service metering capability.
In more detail, cloud computing refers to a computing hardware machine or group of computing hardware machines commonly referred as a server or servers connected through a communication network such as the Internet, an intranet, a local area network (LAN) or wide area network (WAN). Any individual user who has permission to access the server can use the server's processing power to run an application, store data, or perform any other computing task. Therefore, instead of using a personal computer every time to run a native application, the individual can now run the application from anywhere in the world, as the server provides the processing power to the application and the server is also connected to a network via the Internet or other connection platforms to be accessed from anywhere. All this has become possible due to increased computer processing power available to humankind with decreased cost as stated in Moore's law.
Source – wikipedia.org / youtube.com