PWM
A microcontroller pin has two output voltages and nothing in between. Pulse-width modulation is the trick that gets the third: switch fast enough and whatever is downstream — an LED and your eye, a motor and its inductance, an RC filter and a slow ADC — averages the square wave into a level. The pin is still only ever fully on or fully off, which is why it dissipates almost no power doing it. That is the whole reason PWM won over analogue drive for everything from a status LED to a 10 kW inverter.