Memory containing zero space (4)
I believe the answer is:
room
'space' is the definition.
(room is a kind of space)
'memory containing zero' is the wordplay.
'memory' becomes 'rom' (ROM is an example**).
'containing' means one lot of letters goes inside another.
'zero' becomes 'o'.
'rom' enclosing 'o' is 'ROOM'.
(Other definitions for room that I've seen before include "Capacity" , "Enclosed space in a building" , "Latitude" , "See 1" , "Space, area" .)