Meaning: The practice of using a network of remote servers hosted on the Internet to store, manage, and process data, rather than a local server or a personal computer.
Basically, in simple terms, all it means is, you don’t have to spend money on hardware components like servers. You can upload all your content onto a cloud and pay as per your use. If you need more space, pay more. If your requirement is small, pay less.
This shared infrastructure contains large pools of systems that are linked together. Often, techniques are used to maximize the power of cloud computing.
These services are broadly divided into three categories: Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (Paas) and Software-as-a-Service (SaaS).
The name cloud computing was inspired by the cloud symbol that's often used to represent the Internet in flowcharts and diagrams.
A cloud can be private or public. A public cloud sells services to anyone on the Internet. (Currently, Amazon Web Services is the largest public cloud provider.) A private cloud is a proprietary network or a data center that supplies hosted services to a limited number of people. When a service provider uses public cloud resources to create their private cloud, the result is called a virtual private cloud.
Infrastructure-as-a-Service like Amazon Web Services provides virtual server instanceAPI) to start, stop, access and configure their virtual servers and storage
Platform-as-a-service in the cloud is defined as a set of software and product development tools hosted on the provider's infrastructure. Developers create applications on the provider's platform over the Internet.
In the software-as-a-service cloud model, the vendor supplies the hardware infrastructure, the software product and interacts with the user through a front-end portal. SaaS is a very broad market. Services can be anything from Web-based email to inventory control and database processing. Because the service provider hosts both the application and the data, the end user is free to use the service from anywhere.Source: http://searchcloudcomputing.techtarget.com/definition/cloud-computing