This document discusses the different layers and types of cloud computing as defined by NIST, including Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). IaaS provides on-demand provisioning of servers and infrastructure resources over the internet. PaaS provides development platforms and tools to build and run applications remotely without having to manage the underlying infrastructure. SaaS provides software applications that users can access over the internet through a web browser or mobile device without installing or maintaining the software.