Flapjacks are a highly delicious but highly fattening food found throughout the UK. They are usually made with rolled oats, butter, and sugar and/or brown sugar and served with honey. A typical flapjack resembles a breakfast bar or a granola bar and is often cooked in a baking dish. However, there may be times when they are not cooked.
While Americans do use the term flapjack, it usually doesn’t mean the same thing as it does in the UK. What they are most likely trying to say is pancake. A pancake is made by frying pancake batter on a hot skillet. Pancakes are usually made from buttermilk, flour, eggs, salt, sugar and a little baking powder. They end up becoming fluffy due to the baking powder and most diners serve them in a stack where the common practice is to add some butter on top and then drench them with maple syrup.
In other words, here in America the term flapjack and pancake are usually interchangeable and mean the same thing. The only difference being a regional difference. The north and west part of America tend to call them pancakes while the south and southeast parts lean more towards calling them flapjacks.
Another difference is that pancakes can have additional ingredients in them such as blueberries, peanut butter, or chocolate for example. Particular restaurants in America often serve pancakes (and waffles especially) with a variety of different toppings not served in the UK. These could be additional flavors of syrup, whipped cream, powdered sugar, or different sorts of fruit.
Flapjacks are not a common term in Alaska where I live. Although I would definitely try one if and when I go to Europe.