A tattoo in the most common sense is a picture, figure or text drawn in ink (or other pigment) under the topmost layer of skin on an animal or human. In modern times the ink is introduced under the skin by a needle, although some tribal cultures create them by cutting and then rubbing the wound with ink, ashes or other agents. This was probably the original method.

The purposes of tattoos are diverse. Identification, cosmetic, religious and magical uses are the most common. 
Tattooing has been used for thousands of years, as evidenced by Oezti.