In-tray item (4)
I believe the answer is:
'in-tray item' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for memo that I've seen before include "Short note or message" , "Reminder (abbr)" , "A little something to be remembered" , "It will remind" , "- Currie, Br. politician" .)