Piano used in old time musical presentation (5)
I believe the answer is:
opera
'musical presentation' is the definition.
(I've seen this before)
'piano used in old time' is the wordplay.
'piano' becomes 'p'.
'used in' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'time' becomes 'era' (I've seen this before).
'o'+'era'='oera'
'p' going within 'oera' is 'OPERA'.
(Other definitions for opera that I've seen before include "Musical dramatic work" , "One at the Met" , "eg Otello" , "Musical play" , "Carmen, perhaps" .)