The .NET Framework is a software development platform developed by Microsoft. It provides a comprehensive and consistent programming model for building applications, including web, desktop, and mobile applications. The framework includes a large class library known as the Framework Class Library (FCL), as well as runtime environments like the Common Language Runtime (CLR), which executes the applications. The .NET Framework supports multiple programming languages, such as C#, VB.NET, and F#, enabling developers to create a wide variety of applications efficiently.