stupid question

I no this is a dumb question but what EXACTLEY is a cat back exhaust?

self explanitary, exhaust system that bolts on to the catylatic converter to the muffler then the tailpipes

Catalytic converter back. pipe, muffler, and tail pipe.

Here is a pic of what is in a typical cat back system.
http://store.summitracing.com/partdetail.asp?autofilter=1&part=FLO%2D17233&N=700+4294908216+4294908198+4294924928+4294923429+4294922451+4294840138+115&autoview=sku