Does a package (nuget package) contain assemblies or libraries?

I came across two different sources that stated two diferrent things about what a package contains.

Nuget 101 states:

A package contains a complied library with descriptive meta data.

While What is Nuget states:

Package developers who require APIs outside of .NET Standard, on the other hand, create separate assemblies for the different target frameworks they want to support and include all of those assemblies in the same package (which is called "multi-targeting").

So does a package contain an assembly(ies) or a library(ies)? Which is it?