Keeping gold inside the theatre (7)
I believe the answer is:
storage
'keeping' is the definition.
(storage is a kind of keeping)
'gold inside the theatre' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'inside' means one lot of letters goes inside another.
'the theatre' becomes 'stage' (stage is a kind of theatre**).
'or' inserted inside 'stage' is 'STORAGE'.
(Other definitions for storage that I've seen before include "Charge for warehousing" , "Depository space for goods" , "Longer-term laying up" , "Place for putting items away" , "safekeeping" .)