What is .NET standard or "netstandard"?

Purpose:

• Tests whether the developer has experience in .Net framework developments or if they have stagnated in the old framework.
• Tests whether the developer has real world experience in .Net Core and a working understanding of how .Net Standard addresses cross platform binary interaction.

Potential Answers:
A formal specification that represents the APIs that all .Net platforms have to implement.

Common contract that all platforms work towards and as such allows interoperability between these frameworks since they are functionally equivalent.

If the developer can differentiate between .Net Standard and .Net Core it is a really good sign:

• .NET Standard is a specification that covers which APIs a .NET platform has to implement.
• .NET Core is a concrete .NET platform and implements the .NET Standard.