input(":")

Question

in this piece of code:
num=input(":")

is the 'input' statement a variable that we created or is it a system command that automatically gets assigned the value of the user's input?

Answer 1

It is a built-in function.

Python2: https://docs.python.org/2/library/functions.html#input
Python3: https://docs.python.org/3/library/functions.html#input

Answer 2

it is input method which is used to take user input.
it is like cin, scanf etc.