XAML (Extensible Application Markup Language) is an XML-based language used to design user interfaces in Windows applications. It allows for the definition of visual elements such as buttons, menus, and styles, separating the design from the programming logic. It is a key tool in technologies like WPF (Windows Presentation Foundation) and UWP (Universal Windows Platform), facilitating the development of modern applications with attractive and functional interfaces. Its declarative approach makes it accessible for both designers and developers.