Shoshin (初心, also pronounced nyuanshin) is a concept in Zen Buddhism meaning Beginner's Mind. It refers to having an attitude of openness, eagerness, and lack of preconceptions when studying a subject, even when studying at an advanced level, just as a beginner in that subject would.
Mushin (無心; Chinese Wu-hsin; English translation "no-mindedness") is a mental state into which very highly trained martial artists are said to enter during combat. The term is shortened from mushin no shin (無心の心), a Zen expression meaning mind of no mind. That is, a mind not fixed or occupied by thought or emotion and thus open to everything.
Fudoshin (Japanese: 不動心) is a state of equanimity or imperturbability (literally and metaphorically "immovable heart" or "unmoving heart") - a philosophical/mental dimension to a (commonly Japanese) martial art which contributes to the effectiveness of the advanced practitioner.
Fudoshin: A spirit of unshakable calm and determination, courage without recklessness, rooted stability in both mental and physical realms. Like a willow tree, powerful roots deep in the ground and a soft yielding resistance against the winds that blow through it.
Zanshin (Japanese: 残心) is a term used in the Japanese martial arts. It refers to a state of awareness - a state of relaxed alertness. The literal translation is remaining mind.