Final answer:
Pin 13 on most Arduino boards is the pin equipped with a built-in LED, which can be used for easy debugging and visual status indication without the need for an external LED and resistor.
Step-by-step explanation:
The pin with a built-in LED on most Arduino boards is pin 13. When you set up an LED circuit, you usually need a resistor and an external LED; however, thanks to this built-in feature on pin 13, you can test your sketches without the extra hardware. It's a helpful tool for basic debugging and for visually indicating the status of the board during operation.