What is a HDR photo on iPhone 5?

In the iphone 5 photo setting it says HDR, what's the difference between a normal photo and HDR because it takes longer to save? Does it take up more space?

It takes a better quality pic & on the iPhone 4 it takes 3 pics in one

It stands for High Definition Resolution. It basically takes a normal quality photo followed by a better quality one. It's good to have on but make sure you delete the photo copy that you don't want.