The GPLv3 applies to the Program as the GPL defines it. It has a provision, in Section 5, for aggregate works of many programs and is mentioned in the FAQ [1].
> But some argue even typing a file name into a terminal window constitutes a dynamic link.
Who? The FSF holds the opposite. A terminal emulator and a program that runs within it are two separate programs.
[1] https://www.gnu.org/licenses/gpl-faq.en.html#MereAggregation
> "Where's the line between two separate programs, and one program with two parts? This is a legal question, which ultimately judges will decide."
The types of links should be crystal clear from the licence, rather than relying on judges to determine fair use. Companies are likely to avoid the GPL due to the potential risk derived from this lack of clarity.
A terminal emulator and a child process will have different virtual address spaces, so you may choose that as the discriminating factor. A web browser and a web application will share address space. But a web browser and a web application are clearly two separate programs as well.
It isn't really a problem unique to the GPL. Any interpretation of a non-trivial license with conditions will have an element of "I know it when I see it". Software licenses especially due to the level of abstraction.