Mean to trim the end off (3)
I believe the answer is:
par
'mean' is the definition.
(average score on a golf course)
'trim the end off' is the wordplay.
'trim' becomes 'pare' (synonyms).
'the end off' means to remove the last letter.
'pare' with its final letter removed is 'PAR'.
'to' acts as a link.
(Other definitions for par that I've seen before include "Accepted level" , "standard for a pro" , "Norm" , "Rap to get even" , "Average - equality" .)