Truck going round cold polar region (6)
I believe the answer is:
arctic
'polar region' is the definition.
(I've seen this before)
'truck going round cold' is the wordplay.
'truck' becomes 'artic' (short for articulated lorry).
'going round' indicates putting letters inside (some letters go around others).
'cold' becomes 'C' (eg on taps).
'artic' placed around 'c' is 'ARCTIC'.
(Other definitions for arctic that I've seen before include "Relating to North Pole region" , "Northern ocean" , "The frozen north" , "It's cold at the top" , "Of the extreme north" .)