UML (Unified Modeling Language) is a standardized modeling language used to visualize, specify, construct, and document software system artifacts, enabling a systematic approach to analysis, design, and implementation. This document discusses UML's history, building blocks like classes, use cases, relationships, and diagrams for modeling a system's structure and behavior statically and dynamically. The key UML diagram types covered are class, object, component, deployment, use case, sequence, collaboration, state, and activity diagrams.