Music Theory: The understanding of how music works. This is an invaluable tool that gives you the ability to identify your strengths, zero in on what exactly you struggle with, how to overcome any issues you encounter, and gain the skill to wrap your mind around what's going on musically.
Music Psychology: The deeper revelation as to where you need to focus your attention, what's distracting/throwing you off while playing, why you process music the way you do, and how to course correct when you encounter road blocks while practicing and performing.
Musicality: That 6th sense you can develop as a musician, and the process that leads to you discovering your most authentic, personal sound. This can become a determination that guides you and dictates your personal tastes and decisions you make in music.