In Japanese, 無心 means innocent or without knowledge of good and evil. It literally means “without mind.”

無心 is one of the five spirits of the warrior (budo) and is often used as a Japanese martial arts tenet. Under that context, places such as the Budo Dojo define it this way: “No mind, a mind without ego. A mind like a mirror which reflects and dos not judge.” The original term was “mushin no shin,” meaning “mind of no mind.” It is a state of mind without fear, anger, or anxiety. Mushin is often described by the phrase “Mizu no Kokoro,” which means “mind like water.” The phrase is a metaphor describing the pond that clearly reflects its surroundings when calm but whose images are obscured once a pebble is dropped into its waters.

This has a good meaning in conjunction with Chan / Zen Buddhism in Japan. However, out of that context, it means mindlessness or absent-mindedness. To non-Buddhists in China, this is associated with doing something without thinking.
In Korean, this usually means indifference.

Use caution and know your audience before ordering this selection.

More info: Wikipedia: Mushin

虛心坦懐 is a Japanese proverb that means “with an open and calm mind,” “with no preconceived notions,” or “without reservations.”

In some contexts, it can mean frank or candid.

If you want to remind yourself to approach each situation with no preconceptions, this is a good title for you. This can also refer to the ideas of being candid, frank, and straightforward.

一心 can be translated as “one mind,” “single-minded focus,” or “wholehearted devotion,” from Chinese, Japanese Kanji, and old Korean Hanja.

Colloquially or figuratively, it means: wholeheartedly; heart and soul; of one mind; single-mindedness, wholeheartedness; one's whole heart; with the whole mind or heart; one mind in heart.

I'm not kidding, all of those came right from the dictionary for this one title.

In martial arts usage, this term emphasizes total commitment, where intent, attention, and action are unified without distraction.
In Japanese budō, it often conveys wholehearted dedication to practice or principle, whereas in Chinese usage it tends toward inner mental cultivation.

In Buddhism, this can refer to the bhūtatathatā, or the whole of things; the universe as one mind, or a spiritual unity.

In Japanese, this can be the female given name, Hitomi.

鐵心 can be translated as “iron heart,” “steel core,” or “iron mind” in Chinese and Japanese Kanji.

This is not a common term, but I added it here since so many were looking for “iron heart.” This is almost like saying you are without emotions or feelings - a very stoic person. This is not a Buddhist trait.

無心道 is the base title for Mushindo (without mind way). 無心道 is often coupled with a trailing word to make titles like Mushindo-Kai or Mushido-Kempo.

If you are looking for this title, you probably know more than I can tell you about this martial arts style.

靑蓮 is a common title for Blue Lotus.

靑蓮 is often used in a Buddhist context for blue lotus from the Sanskrit “utpala.” This often refers to the clarity and purity of the lotus blue eyes possessed by a Living Buddha. It can also represent the purity of mind (without desire, suffering, fear, etc.).

無事 is a Zen Buddhist term meaning no problem and no trouble.

無事 is the Zen state of perfect freedom from troubles and leaving secular affairs behind.

Sometimes this is used to describe the state of satori and complete tranquility of mind.

Written as 無事に with an extra Hiragana at the end, this becomes an adverb to describe something in the condition of safety, peace, quietness, and without troubles.

無事 (Buji) can also be a given name in Japan.

This has more meaning in the Japanese Zen Buddhist community than in China or Korea, where it can mean “be free” or “nothing to do or worry about.”

禪宗 is one way to title “Zen Buddhism.” Because the original pronunciation of Zen in Chinese is Chan, you'll also see this expressed as Chan Buddhism.

From the Buddhist Dictionary:
The Chan, meditative or intuitional, sect is usually said to have been established in China by Bodhidharma, the twenty-eighth patriarch, who brought the tradition of the Buddha-mind from India. This sect, believing in direct enlightenment, disregarded ritual and sūtras and depended upon the inner light and personal influence for the propagation of its tenets, founding itself on the esoteric tradition supposed to have been imparted to Kāśyapa by the Buddha, who indicated his meaning by plucking a flower without further explanation. Kāśyapa smiled in apprehension and is supposed to have passed on this mystic method to the patriarchs. The successor of Bodhidharma was 慧可 Huike, and he was succeeded by 僧璨 Sengcan, 道信 Daoxin, 弘忍 Hongren, 慧能 Huineng, and 神秀 Shenxiu, the sect dividing under the two latter into the southern and northern schools: the southern school became prominent, producing 南嶽 Nanyue and 靑原 Qingyuan, the former succeeded by 馬祖 Mazu, the latter by 石頭 Shitou. From Mazu's school arose the five later schools.