WPF, or Windows Presentation Foundation, is a graphical subsystem by Microsoft for rendering user interfaces in desktop applications. It uses XAML (Extensible Application Markup Language) to define UI elements, allowing developers to create rich, interactive applications with features like animations, 2D and 3D graphics, and data binding. WPF is part of the Microsoft .NET framework and is designed to take advantage of modern hardware capabilities. It supports a wide range of controls and layouts, making it easier for developers to build visually appealing applications that can run on various Windows operating systems.