QML (Qt Meta-Object Language) is a declarative language designed by The Qt Company for creating fluid, animated, and dynamic user interfaces. It is often used in conjunction with C++ for backend logic, but QML files themselves define the structure, appearance, and behavior of the UI elements. These files use a JavaScript-like syntax combined with object definitions, making them highly readable and efficient for describing complex visual layouts, transitions, and interactions. QML is integral to developing applications using the Qt framework, particularly for cross-platform deployment across desktop, embedded systems, and mobile devices. The language allows developers to easily bind properties, handle signals and slots, and integrate custom components. While the syntax is declarative, QML files are interpreted at runtime, often compiled into an optimized binary format for faster loading in production environments. They are essential for modern, responsive UI development within the Qt ecosystem.