GPIO pin numbering
GPIO pins are a physical interface between the Pi and the outside world. At the simplest level, you can think of them as switches that you can turn on or off. You can also program your Raspberry Pi to turn them on or off (output). The GPIO.BCM option means that you are referring to the pins by the ‘Broadcom SOC channel’ number. The GPIO.BOARD option specifies that you are referring to the pins by their physical pin number.