Cloud Computing can be defined as 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. Companies offering such kinds of cloud computing services are called cloud providers and typically charge for cloud computing services based on usage. Grids and clusters are the foundations for cloud computing.

Types of Cloud Computing
Most cloud computing services fall into five broad categories:

Software as a service (SaaS)
Platform as a service (PaaS)
Infrastructure as a service (IaaS)
Anything/Everything as a service (XaaS)
Function as a Service (FaaS)
These are sometimes called the cloud computing stack because they are built on top of one another. Knowing what they are and how they are different, makes it easier to accomplish your goals. These abstraction layers can also be viewed as a layered architecture where services of a higher layer can be composed of services of the underlying layer i.e, SaaS can provide Infrastructure.