Interwar talks about the years that sat between the First World War and the Second World War. In most of Europe that means from 1918, when the first war ended, to 1939, when the second war began. People use it about life, art, buildings, and politics in those years: interwar fashion, interwar Europe, the interwar period. It is a describing word, a little school-and-history in feel; you will meet it in books and documentaries more than in chat. Though actually, the tidy dates hide a mess: some countries left the first war later, and some felt the second war coming years before 1939. The word does not mean “during a war,” and it does not mean “against war.” It only names that in-between stretch.