This document defines cloud computing and its key characteristics. Cloud computing provides on-demand access to shared computing resources like networks, servers, storage, applications and services that can be quickly provisioned with minimal management effort. It has essential characteristics of on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service. There are three service models - Software as a Service (SaaS), Platform as a Service (PaaS), and Infrastructure as a Service (IaaS). Four deployment models of public, private, community and hybrid clouds are also defined.