NET Core and .NET Standard What is the difference

NET Standard Library is a .NET standard library. . .NET framework and .NET Core, are two different implementations of the standard library.
Some of the first .NET framework. . . Many well known, .NET framework can only run on Windows systems. . Later, Microsoft plans to make .NET can run on other operating systems. So-called cross-system, or cross-platform.
However, some things that are unique to Windows. . . For example D3D. . . On other operating systems, this is not the thing. . . So the .NET framework associated with D3D part, naturally, does not require cross-system, right? Because for the other systems, it is entirely superfluous
Therefore, the portion of the Microsoft .NET framework, you can cross-system to extract out. . . Encapsulated into the standard library, which is part of NET Standard Library. . . No matter on which system, the content of the standard library is completely generic.
But in another operating system, there are some things that are not ah on Windows. . . If only by the content of the standard library, would not no way to operate these "things are not on the Windows"?
So then on the basis of the standard library, developed a NET Core. . . Adding some operations "are not on the Windows stuff" content. .
Simple generalization is. . . . .NET framework and .NET Core there are some parts content is the same, which is part of the same content, it is called the standard library. . . I.e. NET Standard Library. . . And those different parts, respectively called the .NET framework and .NET Core