what are shadow maps and what is a raytraced shadow?

Basically, Poser 4 treats shadows much like textures. The light intensity is mapped or rendered from the perspective of a "shadow-camera" with the same position and orientation as the light source. This shadow map is then applied to all objects in the scene, determining which areas are darker or lighter. A low-resolution shadow map creates fuzzy, blocky, poorly-defined shadows with much pixelation or banding, whereas higher resolutions will produce shadows with sharper, more clearly-defined edges.

Shadow map size can be set from the light's parameter-dial panel. Larger shadow maps consume more resources and take longer to compute, but the results are usually better.

Poser 5 adds the option of raytraced shadows (enabled from the light's properties panel), which uses a different method of calculating light intensity. Raytraced shadows tend to be very sharp.