Mushin means empty mind. It is a state of consciousness that allows the practitioner to transcend their ego and focus purely on the task at hand. This state can be accessed to perform any activity but was highly coveted by samurai so they could be fully engaged in combat. This is more or less a zen term used for what today's athletes would refer to as the zone. Although I'm sure many artists, musicians, craftsmen, and any other person walking a chosen path will understand this term quite well intuitively if not intellectually.