Informal message (4)
I believe the answer is:
memo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">informal message</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for memo that I've seen before include "Office note" , "Inter-office note" , "A brief record of events" , "A little something to be remembered" , "- Currie, Br. politician" .)