This document discusses the history and relationship between .NET Core, .NET Framework, and .NET Standard. It explains that .NET Framework was not platform independent, while .NET Core is cross-platform but lacked Windows Forms and WPF support. .NET Standard was created to define a common set of APIs that can be targeted by frameworks like .NET Core and implemented by frameworks like .NET Framework, allowing libraries to work across platforms. The document notes that .NET Framework 4.7.1 added support for .NET Standard 2.0 by implementing around 200 missing APIs.