Bog product (4)
I believe the answer is:
peat
'bog product' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for peat that I've seen before include "Some got energy from this" , "Fuel cut from bog" , "Partially carbonised vegetable matter used as a fuel when dried" , "Fuel from bogs" , "Fuel from boggy land" .)