Polarization is a property of waves that can oscillate with more than one orientation.Electromagnetic waves, such as light etc exhibit polarization, 
By convention, the polarization of light is described by specifying the orientation of the wave's electric field at a point in space over one period of the oscillation. When light travels in free space, in most cases it propagates as a transverse wave hence the polarization is perpendicular to the wave's direction of travel 

and yeah 
The letters ‘D’ or ‘L’ before the name of any compound indicate the relative configuration of a particular stereo isomer. This refers to their relation with a particular isomer say of glyceraldehyde. Glyceraldehyde contains one asymmetric carbon atom and exists in two enantiomeric forms 

i.e with D-config and L- configuration! 

well i think its an old concept and very confusing one and also not widely accepted! 
its importance is in sugar industry,pharmaceuticals etc. 
and this is used to determine the stereo-chemistry between the isomers of a given molecule!