Many piles (5)
I believe the answer is:
heaps
'piles' is the definition.
('heap' can be a synonym of 'pile')
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for heaps that I've seen before include "Mounds; lots" , "A large number; untidy mounds" , "Lots (of piles?)" , "Mounds, stacks" , "Shape (anag) - lots" .)