Mushin is the essence of Zen and Budo. Mushin literally means the "mind without mind", and it is commonly called "the state of no-mindness".
Mushin is the essence of Zen and Japanese martial arts. It is a state of mind where mind is not fixed on or occupied by any thought or emotion, and is thus connected to the Cosmos.
In Zen on in your daily life, if the impulse is expressed as conscious thought, it is not Zen.
This pure state of mind, of pure mental clarity is produced by the absence of the ego or limited self. A Mushin mind is not an empty mind like an empty shell, on the contrary is it a mind fully present, aware and free.
“Mu” or “emptiness” in Mushin refers to an empty mind in the sense that distractions, preoccupations, fears, worries, are absent and are no more an issue for the mind, whether in combat or in daily life.
The concept of Mushin is identical to the Japanese metaphorical expression “mizu no kokoro” or the “mind like water.” This mental attitude refers to a mind that is in total harmony with the Cosmos that it resembles a still pond of water without any ripples where the surface reflects a clear and perfectly undistorted image of the surroundings, like a mirror.