Stagepin is a Type of Power plug used for high powered lighting instruments most often used on stages and the like. Like the standard edison connector (which your computer is most likely plugged in to), it has three prongs: Hot, Neutral and Ground. Unlike the Edison, however, the three prongs are arranged in a straight line. one may also add that the ground connector on stagepin is noticably longer, helpful for those high wattages...

What the different connectors look like from the front:

Edison
                           
   _____                    ___________________________
  /     \                  |                           |
 /   O   \                 |   O     O          O      |
|         |                |___________________________|
 \ |   | /                   
  \_____/                    
                          
With the plugs being:


    Ground           
                            Hot Ground       Neutral
                     
 Hot    Neutral              

The main difference between Stagepin and edison (besides the shape and size) is the wattage. Most Edison Sockets run anywhere from 10 watts (fluorecsent lights) to 150+ watts. Most stagepin Sockts run at least 15 Amps (around 2000 watts). This is helpful for "throwing" light from a few hundred feet away and still having definite edges.