External Iron Palm usually 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. This usually consists of hitting bags filled with progressively harder material (mung beans, gravel, steel shot, etc.), or hitting and thrusting the hands into large buckets filled with training materials. Some methods require more “modern” methods such as replacing the bean-filled bags with a thick telephone book.
It is also used to refer to a style of training that is strictly “external” (meaning without any internal component). Some external methods involve only hitting the bag and don’t necessarily use dit da jow or any qigong exercises. It is worth mentioning however that many people believe that without the use of dit da jow the hand may become disfigured over time since the microtrauma that occurs during each training session may not fully heal before the next training session. An often cited example is the knuckles of someone who practices traditional makiwara without using any liniment; their knuckles become enlarged over time.
Purely external styles that don’t use jow or have a qigong component are sometimes thought of as being not as “complete” as the styles that include an internal component. They still develop the ability to strike hard.
Just as there are purely external systems, there are also purely internal systems that seek to the palm without actually doing physical conditioning.