Talk about finishing up in the open spaces (4)
I believe the answer is:
gaps
'the open spaces' is the definition.
(I've seen this in another clue)
'talk about finishing up' is the wordplay.
'talk' becomes 'gas' (gas can mean to chat).
'about' is an insertion indicator.
'finishing' suggests the final letters (the letter which finishes the word).
The final letter of 'up' is 'p'.
'gas' enclosing 'p' is 'GAPS'.
'in' acts as a link.
(Other definitions for gaps that I've seen before include "Breaks or openings as in hedge or fence" , "Breaks, spaces" .)