OpenCV - Doubt in a line.

[ThomasL]

Did you check what cv2.waitkey() is doing?
If not look here!

The function waitKey waits for a key event infinitely (when {delay}>= 0 ) or for delay milliseconds, when it is positive. Since the OS has a minimum time between switching threads, the function will not wait exactly delay ms, it will wait at least delay ms, depending on what else is running on your computer at that time.

It returns the code of the pressed key or -1 if no key was pressed before the specified time had elapsed.