This document discusses cloud computing. It defines cloud computing as using computer resources that are delivered as a service over the Internet. These resources include hardware, software, storage and databases. Users can access these resources from anywhere as needed rather than having the resources provided locally. The document then discusses key characteristics of cloud computing like multi-tenancy, scalability, on-demand resources and reliability. It also discusses different types of cloud models including public, private and hybrid clouds. Finally, it provides examples of cloud computing platforms like Amazon Web Services and Google Application Engine.