.net is a collection of multiple programming languages. It has some predefined classes

.NET is a programming framework created by Microsoft that developers can use to create applications more easily. it is set class libraries consisting of pre-written code called “classes” that provides many functionalities for developing applications.In .Net framework everything in organised into groups called “namespace”.So .Net Framework is the collection of Assemblies to support the .Net application development and .Net application execution.In short, .NET Framework provides an environment for building, developing and running web services and other applications. It consists of three distinct technologies:

1. Common Language Runtime (CLR)
2. Framework Based Classes
3. User interface program (ASP.NET and Winforms)

So what is .Net? It is not a Language. It is not an operating system. It is a platform to execute .Net applications.