Summary on top (5)
I believe the answer is:
recap
'summary' is the definition.
(recap is a kind of summary)
'on top' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'top' becomes 'cap' (cap is a kind of top).
're'+'cap'='RECAP'
(Other definitions for recap that I've seen before include "Go over the main points again, in short" , "Go over things again" , "Summarise at the end" , "Run through again (Inf)" , "Summary (abbr.)" .)