Printer's error in quality poem (4)
I believe the answer is:
typo
'printer's error' is the definition.
(I've seen this before)
'in quality poem' is the wordplay.
'in' indicates a hidden word.
'TYPO' can be found hidden inside 'quality poem'.
(Other definitions for typo that I've seen before include "Character flaw" , "Mistake in printed matter, in short" , "Keyboard slip-up" , "False character" , "Printer's error" .)