Class Diagram Definition A class diagram is a type of UML (Unified Modeling Language) diagram that visually represents the structure of a system by showing its classes, attributes, methods, and relationships. It serves as a blueprint for how different parts of an object-oriented system interact and organize data. Class diagrams are fundamental in system design because they bridge the gap between real-world concepts and code implementation. This helps developers, analysts, and stakeholders understand how the system’s components are connected and how they collaborate to perform various functions.