Something maybe in freezer that is keeping cold (3)
I believe the answer is:
ice
'something maybe in freezer' is the definition.
(a freezer might contain ice)
'that is keeping cold' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'keeping' is an insertion indicator.
'cold' becomes 'c' (eg on taps).
'ie' enclosing 'c' is 'ICE'.
(Other definitions for ice that I've seen before include "Cooler" , "Frozen water; kill (slang)" , "Skating surface" , "A state of water" , "Solid H2O" .)