While many talk about the cloud, few actually understand it. Three organizations' definitions come to the forefront when defining the cloud: Gartner, Forrester, and the National Institutes of Standards and Technology (NIST). Although both Gartner and Forrester provide definitions of cloud computing, the NIST definition is concise and uses industry-standard terms. This article takes an in-depth look at the NIST definition of cloud computing. Each of the NIST definition's points is defined in greater detail, and examples of cloud-based technologies will help the reader gain a better understanding of the cloud. Cloud computing is defined as "a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction. This cloud model promotes availability and is composed of five essential characteristics, three service models, and four deployment models." The author discusses these five characteristics, three service models, and four deployment models. (Contains 9 endnotes.)