Tramp stamp is the common term for a tattoo located on the lower back. It is also called a lower-back or lumbar tattoo. These tattoos often are associated with the promiscuity of a woman, which is where the common term for this kind of tattoo comes from.
The term was originally used to describe any kind of tattoo, since tattoos look as if their designs are stamped onto skin. The lower-back tattoo rose in popularity in the early 2000s because of their use by a number of celebrities, the trend of low-rise jeans, and the popularity of crop tops. While these tattoos are most often seen on women, men are not exempt from getting lower-back tattoos.