Cloud computing is a model that provides on-demand access to shared configurable computing resources like servers, storage, databases, networking, software, analytics and more over the internet. It has key characteristics of on-demand self-service, broad network access, resource pooling, rapid elasticity and measured service. There are three cloud service models - SaaS, PaaS and IaaS and four deployment models - private cloud, community cloud, public cloud and hybrid cloud. Cloud computing offers advantages of scalability, affordability and security.