A stylus is any type of pen that is detected as an active pen by Microsoft, it comes down to the diameter of the point on the stylus. This diameter is:  1.8mm - 3mm. CommBox Classic Stylus has dual ends, 1 is 2.8mm and the other is 8mm which acts as a finger touch point.
 
The advantage of having a stylus is that windows detects it and switches to annotation rather then having to change to it in settings, if you are marking up a document.