Tax-free zone (5,7)
I believe the answer is:
black economy
'tax-free zone' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for black economy that I've seen before include "untaxed zone" , "Tax-free zone" , "A nation's illegally undeclared income" , "It produces illegally undeclared income" , "Unrecorded and untaxed dealings" .)