Windows Runtime is a platform developed by Microsoft that allows developers to create applications for the Windows operating system. It provides a set of APIs and tools that enable apps to run on various devices, including PCs, tablets, and phones. This framework supports multiple programming languages, such as C#, C++, and JavaScript, making it accessible to a wide range of developers. The Windows Runtime is designed to offer a consistent experience across different devices, ensuring that applications can share code and functionality. It also includes features like asynchronous programming and UI controls, which help developers create responsive and user-friendly applications.