Did you mean the shader or the find?
because i didn't make the shader i found what ambient light dir did.
I suppose saying that now doesn't make a diffrence though. rep can't be un-done really.
Ambient light is the amount of extra light shined (is that how you say it?) on the side of an object not facing a light source (in this case the sun), if it is facing a light source the ambient light is added on to the original light.