Records terrible slog (4)
I believe the answer is:
logs
'records' is the definition.
(I know this)
'terrible slog' is the wordplay.
'terrible' indicates an anagram.
'slog' anagrammed gives 'LOGS'.
(Other definitions for logs that I've seen before include "Written records of events on board" , "Written record of a voyage" , "Firewood; records" .)