In writing about the science of martial arts of the individual school of Two Swords in the Scroll of Emptiness, the meaning of emptiness is that the realm where nothing exists or cannot be known is seen as empty.
Of course, emptiness does not exist. Knowing of nonexistence while knowing of existence is emptiness.
Wrongly Viewed among people of the world, not understanding anything is itself considered emptiness. This is not real emptiness; it is all delusion.
In the context of this science of martial arts as well, in carrying out the way as a warrior, not knowing the laws of warriors is not emptiness; being confused, one may call a state of helplessness emptiness, but this is not real emptiness.
Warriors learn military science accurately and go on to practice the techniques of martial arts diligently. The way that is practiced by warriors is not obscure in the least. Without any confusion in mind, without slacking off at any time, polishing the mind and attention, sharpening the eye that observes and the eye that sees, one should know real emptiness as the state where there is no obscurity and the clouds of confusion have cleared away.
As long as they do not know the real way, whether in buddhism or in worldly matters, everybody may think their path is sure and is a good thing but from the point of view of the straight way of mind, seen in juxtaposition with overall social standards, they turn away from the true Way by the personal biases in their minds and the individual warps in their vision. Knowing that mentality, taking straightforwardness as basic taking the real mind as the Way, practicing martial arts in the broadest sense, thinking correctly, clearly, and comprehensively, taking emptiness as the Way, you see the Way as emptiness.
In emptiness there is good but no evil. Wisdom exists, logic exists, the Way exists, mind is empty.

- Musashi Miyamoto, 12 May 1645