Little piece back in concert, sacred music (5)
I believe the answer is:
motet
'sacred music' is the definition.
(I've seen this before)
'little piece back in concert' is the wordplay.
'little piece' becomes 'mote' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'back in' suggests the final letters (the 'back' of the word).
The final letter of 'concert' is 't'.
'mote'+'t'='MOTET'
Can you help me to learn more?
(Other definitions for motet that I've seen before include "Musical composition" , "Short sacred choral piece" , "Piece for choir" , "Unaccompanied choral composition with sacred lyrics" , "Anthem or church cantata" .)