Amount of land about to be held in a restricted zone? (7)
I believe the answer is:
acreage
'amount of land' is the definition.
(I've seen this before)
'about to be held in a restricted zone?' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to be held in' means one lot of letters goes inside another.
'restricted zone?' becomes 'cage' (place which traps or restricts someone).
'a'+'cage'='acage'
're' inserted inside 'acage' is 'ACREAGE'.
(Other definitions for acreage that I've seen before include "Number of area measurements" , "expanse" , "Amount of land" , "Area measure" , "Surface area" .)