This document defines cloud computing and its basic concepts. Cloud computing allows users to access applications over the internet as utilities. There are four deployment models - public, private, hybrid, and community clouds. The three main service models are Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). IaaS provides fundamental computing resources, PaaS provides development platforms, and SaaS provides applications to end users. The cloud offers advantages like lower costs, improved performance and collaboration, but also disadvantages such as internet dependence and potential security issues.