"Big Three" meeting site (5)
I believe the answer is:
yalta
'big three meeting site' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for yalta that I've seen before include "Conference location" , "Site of the Allied conference in 1945" , "Crimean resort and seaport" , "Crimean resort city" , "Nineteen forty five conference site" .)