Audition tape (4)
I believe the answer is:
demo
'audition tape' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for demo that I've seen before include "Protest march (sl.)" , "Brass instrument valve" , "In brief, a public event as of protest under dome" , "Show" , "Eg, protest march" .)