The meaning of Destreza. Here is a definition from the Pacheco de Narvaez student book

A summary of True Destreza, and the way of how to learn the true movements in battle, the limitations of Christians, and the actual movements, 1688.

Chapter 1
What is Destreza

Destreza is an intellectual teaching, without extravagant moves. Destreza is both theoretical and practical. In theory it means more than just the teaching of calculations; it gives one certain understanding that allows not to omit other needed things, and it does not urge one to rely on God. It has to be pointed out that here we are talking about the Holy Theory.
Not whole doctrine and movements are applied, since not all of them are not known in particular, not even all that are known are applied; they are not represented in the usual way, because it depends on dexterity, delay, strength or accuracy. For this, it is necessary to hone the skill, speed, and execution itself, but it is not so easy to do it, therefore these two things are interconnected in one movement. Both of them require skill. Consequently, we are compelled to develop it, and since this teaching is speculative one has to follow the principles that are true for everybody either one is lazy, strong, or lean.