What is Terroir?

There are few things Anglo-Americans distrust more than foreign words. Not words of foreign origin, you understand. English is the ultimate melting pot, with hardly a word unborrowed from somewhere else. But the problem is words that persistently, stubbornly stay foreign. Words that are, gasp, italicised. Why would an honest word not want a British or American passport? It must be because it has something to hide.