Please help me that, what's happening in line 9

def add(num1, num2, *args):
    total = num1 + num2
    for arg_item in args:
        total += arg_item
    return total
print(add(6, 2))
print(add(6, 2, 10, 1, 4))
print(add(6, 2, 10, 1, 4, 100, 50, 1))
print(add(6))    # what is happening here?