The Microsoft .NET Framework is a software development platform designed to create and run applications on Windows. It provides a large library of pre-built code, known as the Base Class Library, which developers can use to build applications more efficiently. The framework supports multiple programming languages, allowing developers to choose the one that best fits their needs. Additionally, the .NET Framework includes a runtime environment called the Common Language Runtime (CLR), which manages the execution of applications. This ensures that programs run smoothly and securely, handling tasks like memory management and exception handling automatically.