What exactly is Python multiprocessing Module's .join() Method Doing?

Question

Learning about Python Multiprocessing (from a PMOTW article) and would love some clarification on what exactly the join() method is doing.

In an old tut

Answer 1

Without the join(), the main process can complete before the child process does. I'm not sure under what circumstances that leads to zombieism.

The main purpose of join() is to ensure that a child process has completed before the main process does anything that depends on the work of the child process.

The etymology of join() is that it's the opposite of fork, which is the common term in Unix-family operating systems for creating child processes. A single process "forks" into several, then "joins" back into one.