NET Framework (pronounced as "dot net") is a software framework developed by Microsoft that runs primarily on Microsoft Windows. It includes a large class library named as Framework Class Library (FCL) and provides language interoperability (each language can use code written in other languages) across several programming languages. Programs written for .NET Framework execute in a software environment (in contrast to a hardware environment) named the Common Language Runtime (CLR). The CLR is an application virtual machine that provides services such as security, memory management, and exception handling. As such, computer code written using .NET Framework is called "managed code". FCL and CLR together constitute the .NET Framework. The latest .Net framework is 4.8 (2019) you can download this software from a direct link and install it offline internet. (link bellow)
.NET Framework includes the Common Language Runtime (CLR). It serves as the execution engine of .NET Framework and offers many services such as memory management, type safety, exception handling, garbage collection, security and thread management. All programs written for .NET Framework are executed by the CLR. Programs written for .NET Framework are compiled into Common Intermediate Language code (CIL), as opposed to being directly compiled into machine code. During execution, an architecture-specific just-in-time compiler (JIT) turns the CIL code into machine code. With Microsoft's move to .NET Core, the CLI Virtual Execution System (VES) implementation is known as CoreCLR instead of CLR.
Source : Microsoft - Wikipedia