Cloud computing is Internet ('Cloud') based development and use of computer technology ('Computing'). The cloud is a metaphor for the Internet (based on how it is depicted in computer network diagrams) and is an abstraction for the complex infrastructure it conceals. It is a style of computing where IT-related capabilities are provided “as a service”, allowing users to access technology-enabled services from the Internet ("in the cloud") without knowledge of, expertise with, or control over the technology infrastructure that supports them. According to the IEEE Computer Society it "is a paradigm in which information is permanently stored in servers on the Internet and cached temporarily on clients that include desktops, entertainment centers, table computers, notebooks, wall computers, handhelds, etc
Utility computing is a metered service where computing or storage resources are provided on a needed basis similar to the way public utilities (water, electricity, telephone, etc.) are provided to homes and paid for as they are used. The purest form of utility computing requires two service characteristics metered billing and dynamic resource allocation. Customers of utility computing are not billed for a specific computer or server but are billed just for the computing or storage facilities and cycles used. In the simplest terms, utility computing implies the capability to use more resources temporarily and on-demand during peak periods.
Grid computing allows the virtualization of distributed computing and data resources such as processing, network bandwidth and storage capacity to provide a unique system image, granting users and applications access to vast IT capabilities.
Software as a service (SaaS)
A software application delivery model where a software vendor develops a web-native software application and hosts and operates the application for use by its customers over the Internet. Customers pay for using the software itself, not for owning the software.