Irezumi is a Japanese word that refers to the insertion of ink under the skin to leave a permanent, usually decorative mark; a form of tattooing.
The word can be written in several ways, each with slightly different connotations.
The most common way of writing irezumi is with Chinese characters who literally means to "insert ink".
These characters (also pronounced bunshin) suggest "decorating the body". Bunshin is more esoteric, being written with the characters for "stay" or "remain" and "blue" or "green", and probably refers to the appearance of the main shading ink under the skin.

Tattooing for spiritual and decorative purposes in Japan is thought to extend back to at least the Jomon or paleolithic period (approximately 10,000 BC).
Some scholars have suggested that the distinctive cord-marked patterns observed on the faces and bodies of figures dated to that period represent tattoos, but this claim is by no means unanimous.
There are similarities, however, between such markings and the tattoo traditions observed in other contemporaneous cultures.

In the following Yayoi period (c. 300 BC-300 AD) tattoo designs were observed and remarked upon by Chinese visitors.
Such designs were thought to have spiritual significance as well as functioning as a status symbol.

Starting in the Kofun period (300-600 AD) tattoos began to assume negative connotations.
Instead of being used for ritual or status purposes, tattooed marks began to be placed on criminals as a punishment (this was mirrored in ancient Rome, where slaves were known to have been tattooed with mottoes such as "I am a slave who has run away from his master").

Source: Wikipedia