What is it? #

Conditional statement that runs a particular chunk of code if the file is called directly.

Structure #

def main():
    ...
    # oftentimes, calls to functions defined higher up in the script

if __name__ == '__main__':
    main()

__name__ #

print __name__

# __main__

Whenever Python runs, it sets a bunch of special variables, including __name__. A Python script that is called directly causes __name__ to be set to __main__.