Serial Monitor

The serial monitor is an integrated part of the Arduino IDE (integrated development environment) is a console for your microcontroller. This is where communication between you and your microcontroller can happen, when your program is running. An example of this could be you telling your Arduino to turn on a LED, or the Arduino telling you the distance measured with an ultrasonic sensor.

If you are using a Raspberry Pi you use the console to communicate instead. Depending on what language and IDE you are using, it will look a bit different, but they all function the same.