Stacks milk products metres to the left (6)
I believe the answer is:
myriad
'stacks' is the definition.
(both can mean a large amount)
'milk products metres to the left' is the wordplay.
'milk products' becomes 'dairy' (I've seen this before).
'metres' becomes 'm'.
'to the left' is a reversal indicator (reading from right to left).
'dairy'+'m'='dairym'
'dairym' back-to-front is 'MYRIAD'.
(Other definitions for myriad that I've seen before include "Large indefinite number" , "Countless - very large but indeterminate number" , "Too numerous to be counted" , "Immense number found by dim ray" , "Numberless" .)