Strength.

Strength: the quality or sate of being strong. A good or beneficial quality or attribute of a person or thing. A word often used to describe what a person is best or strongest at. Also it could be used to resemble how physically strong a person is or a how strong a person is mentally as well. For me, i use strength to resemble how strong i am mentally. Although i do use it to describe how strong i am physically as well.