Final exam over, covered in mistakes (6)
I believe the answer is:
tripos
'final exam' is the definition.
'tripos' can be an answer for 'exam' (tripos is a kind of exam). I'm not sure about the 'final' bit.
'over covered in mistakes' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'covered in' means one lot of letters goes inside another.
'mistakes' becomes 'trips' (trip is a kind of mistake).
'o' inserted within 'trips' is 'TRIPOS'.
Can you help me to learn more?
(Other definitions for tripos that I've seen before include "important examination" , "university exam" , "Final honours exam for Cambridge BA" , "Cambridge honours examination" .)