UML, or Unified Modeling Language, is a standardized way to visualize the design of a system. It uses various diagrams to represent different aspects of a project, such as its structure and behavior. This helps developers and stakeholders understand how the system works and how its components interact with each other. By using UML diagrams, teams can communicate more effectively and ensure everyone is on the same page. Common types of diagrams include class diagrams, which show the system's classes and their relationships, and sequence diagrams, which illustrate how objects interact over time.