python3 what is __main__ - name for code example

Example: __name__== __main__ in python

# If the python interpreter is running that module (the source file)
# as the main program, it sets the special __name__ variable to have
# a value “__main__”. If this file is being imported from another 
# module, __name__ will be set to the module’s name.
if __name__=='__main__':
  # do something