The Arduino distinguishes between “digital” and “analog” outputs. As was the case with inputs, the nomenclature used for outputs is a little misleading. Arduino's digital outputs are better called “Boolean” or “logical” outputs. Arduino “analog” outputs are actually a special form of a Boolean output. (We discuss analog outputs in the following section.) As we did with inputs, we will use the nomenclature used in the Arduino literature to avoid confusion.

An Arduino digital output is one that can be set to one of two levels: HIGH or LOW. When a digital output is set HIGH, it will output a voltage approximately equal to the power supply voltage. When it is set LOW, it will output a voltage approximately equal to zero volts.

All of the examples we have seen so far have used digital outputs, so there's not much more to say.