External Iron Palm refers to the physical component of iron palm training. It is the hand conditioning that allows the hand to become physically tough and able to deliver and absorb a large amount of damage.
It is also used to refer to a style of iron palm that is strictly “external” (meaning without any internal component). Some external iron palm methods involve only hitting the iron palm bag and don’t necessarily use dit da jow or any qigong exercises. They are sometimes thought of as being not as “complete” as iron palm styles that include an internal component.