The record is between 100 and 500 (4)
I believe the answer is:
disc
'the record' is the definition.
(eg a CD, compact disc)
'is between 100 and 500' is the wordplay.
'between' means one lot of letters goes inside another.
'100' becomes 'C' (Roman numeral).
'and' means one lot of letters go next to another.
'500' becomes 'D' (Roman numeral for 500).
'c' after 'd' is 'dc'.
'is' inserted into 'dc' is 'DISC'.
(Other definitions for disc that I've seen before include "Back part" , "something moving in the spine" , "Flat thin circular body" , "Spine cartilage layer" , "Flat round plate" .)