They are a puffy pancake baked in a hot metal or cast iron pan. The batter is poured over hot sizzling butter, placed immediately in the oven where they puff up and then fall as they cool.  German pancakes are similar to popovers and Yorkshire puddings.  Yorkshire puddings however are prepared using meat juices and fats and are served with a roasted meat with gravy.  Poffertjes are also similar  but made with yeast.  A couple other names they are known by are dutch babies, bismarks, a Dutch puff or large American popovers.