What is the main purpose of the .NET Standard interface?

The main purpose of .NET Standard is to define a unified set of APIs that must be supported by all .NET implementations (e.g., .NET Framework, .NET Core, Xamarin). This allows creating libraries that are compatible across different .NET platforms without writing platform-dependent code.

Example: if you create a library targeting .NET Standard 2.0, it can work on .NET Framework 4.6.1, .NET Core 2.0, and other platforms supporting this standard.