Neigong (Nei = internal, Gong = practice, skill) are specialised exercises (jibengong or others) to develop more internal power and health by cultivating Jing, Qi and Shen. If it does not include these components altogether in one package, it's NOT Neigong. The opposite of Neigong is Waigong (Wai = external), exercises to develop more power ... and health by using the muscles, whereas in Neigong next to Jing, Qi and Shen it is more about using the Tendons and ligaments. Neigong for martial purposes develops Jin (Ging) and Waigong develops Li (Lik).
Basically Waigong is what modern athletes do. Some are also practicing to strengthen their bones, but it is just like Thai boxing and much of what mixed martial artists do. It is called "Wai" (external) because when they are practicing it, everyone can see it obviously as their body moves (e.g. running, jumping, punching, kicking). Neigong, on the other hand, when practiced, is not so obvious as most of the process and important parts are about Qi, Shen, Jing and developing the Universal Force and Yi (intent) and none of them can be seen externally. Hence it is called "Nei" (internal).
Is Qigong the same as Neigong? Is the "qi" in Qigong the same as the "qi" in Neigong? The "qi" in Neigong is a VERY SPECIFIC thing, and it cannot be practiced without also practicing Shen, Yi and Jing. So there's no point to practice just our "qi". If the "qi" in Qigong means "breathing", then Qigong is just an ordinary aerobic exercise, thus NOT Neigong at all. YES to be clear Qi in Neigong does not refer to breathing period!
So why practice Neigong? Why don't we just practice Waigong or usual sports? Wouldn't it also automatically make our internal body healthier and stronger? Because Neigong cultivates our internal organs, in general it makes us much healthier. And especially when it comes to power purposes for Martial Arts, Neigong enables us to attain power up to 3-4 times bigger than our muscles are usually capable of. Without proper instruction and cultivation, of course this can’t be reached. In the IWKA Neigong program we make sure that the target to develop real Huan Yan Li (Wan Yuen Lik) is reached.