Stacks (5)
I believe the answer is:
heaps
'stacks' is the definition.
(I know this)
This is the entire clue.
(Other definitions for heaps that I've seen before include "A large number; untidy mounds" , "Shape (anag) - lots" , "Mounds; lots" , "Mounds, stacks" , "Lots (of piles?)" .)