ummm noob question.... what exactly are cat backs?

and my catalitic converters are clogged... i know that the best route is to get a down pipe & mid pipe, and that will get rid of this problem forever... what size down/mid pipe do i need for a tii fc?

what would the best route to take?

 

cat-back exhaust are mufflers with piping that bolts up to the sotck catalytic converter

3 in dp and mp is the typical setup for a turbo fc