The summary is exact but incomplete (6)
I believe the answer is:
precis
'the summary' is the definition.
(precis is a kind of summary)
'is exact but incomplete' is the wordplay.
I cannot quite understand how this works, but
'is' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for precis that I've seen before include "Synopsis, summary" , "Sketchy summary" , "Summary, short version" , "Abridgment (of text)" , "Summary of the main points" .)