.Net Core - Difference between .Net Standard and .Net Core

I try to explain and clear up the difference between a .Net Standard Class Library and a .Net Core Class Library and when to use which Good reading: https://blogs.msdn.microsoft.com/dotnet/2016/09/26/introducing-net-standard/ .Net Standard Reference Table: https://docs.microsoft.com/en-gb/dotnet/standard/net-standard