Paper pack (4)
I believe the answer is:
ream
'paper pack' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ream that I've seen before include "480 sheets of paper" , "Quantity of paper, about 500 sheets" , "Twenty quires of paper" , "500 sheets, perhaps" , "Many bits of paper" .)