And for shadows and for ambient occlusion. You can have depth-mapped shadows of course instead of raytraced, but they are less more accurated and ambient-occlusion doesn't work at all without raytracing in poser7. Raytracing is a technique that's older than Poser, but only available in poser since version 5.
"Simply" said it's an algorithm that takes actually calculates a ray of light that comes from a pixel in the renderscreen and hits the camerapoint. The algorityhm looks at all the objects and figures and their materialshader and the lights in the scene, and by calculating the angles between the lights, the other object, the camerapoint and considering all the materialsettings, it defines the actual brightness and colour of the pixel. If the ray hits nothing it gets the colour of the background, if the ray is blocked by objects and can't reach a light it is a shadow.  In fact it is pure light physics.

-How can you improve things when you don't make mistakes?