Was released in the year 2002 and along allows to build Windows Applications
It will not get new features but can still be used to build Windows only applications and App Modules that are only supported by .NET Framework (WPF, Windows Forms)
The last version is 4.8
.NET Core
It is an reinterpretation of the .NET Framework with emphasis on cross platform compatibility
The last version is 3.1
.NET
It is the continuation of the .NET Core project under a new name which will be followed from version 5 onward
v4 was skipped as to not cause confusion with .NET Framework 4
.NET Standard
Set of common Base Class Libraries (BCL) which can be used across .NET implementations (.NET Framework, .NET Core, Xamarin, Mono) and supported OS
It is an temporary solution that is used to bridge the gap between the various .NET implementations
If our project is build on a newer Standard then we have access to a lot of new APIs but they will not run on very old versions of .NET
.NET Standard will go away once .NET 6 is released as it is will merge all the BCLs implementation into a common BCLs that can be used across implementations