.NET is a software framework developed by Microsoft that includes a runtime environment, class libraries and tools to develop various types of applications. The .NET Framework provides a common language runtime (CLR) that compiles code into an intermediate language and provides services like memory management and security. It also includes a base class library for developing Windows forms, web forms, web services and more using languages like C# and Visual Basic. .NET aims to provide a unified platform for developing desktop, web and mobile applications using common languages and libraries.