Pulse Width Modulation
Open-Source Electronics Platform
If we consider simple meaning of it, it is modulating pulse width.
Its a technique for getting analog results with digital means by changing the portion of the time the digital signal spends on versus the time that the signal spends off. The duration of "on time" is called the pulse width. By modulating or changing the time signal remains ON i.e. pulse width, we can have varying analog voltages.
We have used Arduino board(one of the new technologies) to implement the same. The LED attached to the board slowly blows and dims showing analog output and the input to the board is a digital signal.