I have heard of this several times but have been able to find out what it is. I have a good idea but i just wanted to clear things up a bit. so what exactly is it?

If I'm not mistaken, its where you hold your model under a light to see what it hits and what is visible and what is not, so you know what others will see when your model is displayed

It's called "zenithal lighting," and it's what most figure painters use to paint highlight their figures. You can google it for more information. As Steeve said, you hold you figure under a directed light source over the head replicating the sun at its zenith or highest point. This illuminates where you will want to place your highlights and shadows. For more dramatic effects, you could hold the light at any angle to replicate a setting or rising sun, a street lamp, a table lamp, a candle or torch being held at arm's length, etc.