It's played when there's room for love (5)
I believe the answer is:
cello
'it's played' is the definition.
(cello is a kind of musical instrument)
'room for love' is the wordplay.
'room' becomes 'cell' (cell is a kind of room).
'for' means one lot of letters go next to another.
'love' becomes 'o' (love means zero in tennis).
'cell'+'o'='CELLO'
'when there's' acts as a link.
(Other definitions for cello that I've seen before include "Large stringed instrument" , "Bass stringed instrument" , "Music-maker" , "Casals' instrument" , "It's bigger than a viola, but smaller than a double bass" .)