Neigong is a focus. It is like a koan.

It pays attention to how an action is performed rather than the action itself.

Imagine throwing a punch?
Neigong addresses what the body does in order to produce the punch.
It re-trains the framework to deliver power from the whole-unit rather than the shoulder, waist and leg.

Each neigong is different. It has a particular emphasis.
Neigong is internal, with most of the work occurring unseen.
The body looks to undulate as you move.