Default Namespace (The GNU Awk User’s Guide)

From Get docs

15.3 The Default Namespace

The default namespace, not surprisingly, is awk. All of the predefined awk and gawk variables are in this namespace, and thus have qualified names like awk::ARGC, awk::NF, and so on.

Furthermore, even when you have changed the namespace for your current source file (see section Changing The Namespace), gawk forces unqualified identifiers whose names are all uppercase letters to be in the awk namespace. This makes it possible for you to easily reference gawk’s global variables from different namespaces. It also keeps your code looking natural.