These pretties are called popovers because they do pop over the tin during baking process. From what I read on wikipedia, Americans addapted the recipe from British's Yorkshire pudding.
They look really similar to muffin, but once you have a bite, you'll know the difference. Compared with muffins, popovers use more eggs in the batter, are baked in higher temperature, and take around 30 to 45 minutes (sometimes longer) to bake. Just like muffins, popovers can also be served as dessert (sweet) or with another meal (savory).