What is Python __ main __? code example

Example 1: python main

def main():
    print("Hello World!")

if __name__ == "__main__":
    main()

Example 2: how to define main in python

# Defining main function 
def main(): 
    print("hello World") 
  
  
# Using the special variable  
# __name__ 
if __name__=="__main__": 
    main()