What does it mean in python: if __name__ == "__main__"

my_app.py

# In the programm my_app.py we only import
# the module "test.py" from the folder "modules"

import modules.test

test.py

# Create a folder with name "modules" and put this file there, then run separately
#    python my_app.py
#    python modules/test.py
# and compare the output.
#
# REFERENCES:
#    https://docs.python.org/3/library/__main__.html?highlight=__name__
#    https://docs.python.org/3/reference/import.html?highlight=__name__#__name__

print('PART 1\n'
      'This code will be executed in any case.\n')

if __name__ == '__main__':
    print('PART 2\n'
          'The code will be executed only if we run the file as a separate program. '
          'In this case a built-in variable\n__name__ =', __name__, '\n')
else:
    print('PART 3\n'
          'This part will be executed only when we import the file as a module in other program. '
          'In this case the built-in variable __name__ will be assigned to the name of the file '
          'as we specify it with the import statement. In my case I named the file as "test.py" '
          'and put it in a folder "mudeles", then imported in "my_app.py". Therefore:\n'
          '__name__ =', __name__, '\n')

About "main"
About name

    git clone https://gist.github.com/ec2895b7c47f89e72d51fefb718e3e2c.git
    cd ec2895b7c47f89e72d51fefb718e3e2c/
    mkdir modules
    mv test.py modules/
    python my_app.py
    python modules/test.py

    $ tree 
    .
    ├── modules
    │   └── test.py
    └── my_app.py