What are the meanings of the barcodes on business reply mail?

This is probably the most boring question I’ve ever asked (and evidence that I’m up too late), but I recently got the iPhone Red Laser app which reads barcodes, and so now I’m interested in barcodes and I’ve been reading about them (and scanning anything with a barcode I can find and watch the name of the product show up on the phone…so cool…)

Anyway, business reply mail has three sets of bars on and it seems to be hard to find info on what they mean:

http://www.northwestern.edu/univ-relations/publications/content_images/businessreply-sample.gif

What are the meanings of the thick bars on the right, the ones on the top, and the ones on the bottom?