This document provides an overview of cloud computing, including definitions, models, and applications. It begins with definitions of cloud computing from various experts and the National Institute of Standards and Technology (NIST). It then covers NIST's essential characteristics, service models (SaaS, PaaS, IaaS), deployment models (private, public, hybrid, community), and reference architecture including the roles of cloud consumers, providers, brokers, auditors, and carriers. The document also discusses applications of cloud computing such as ECG analysis, protein structure prediction, and social networking. It concludes with typical commercial terms of service agreements between cloud providers and consumers.