"Big Three" meeting site
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">big three meeting site</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 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" .)