back tat 

A tattoo, primarily done by females, on the backside usually in the small of the back.

Did you see that back tat she was sporting? It looked like some kind of doodle.

back tat by Elmer Fudd October 27, 2003

Lower back tattoo 

A lower back tattoo (also referred to as a "tramp stamp" or "California license plate") is a tattoo placed in center of the human lower back. Beginning in the early 2000s, this particular type of tattoo became common among young women. Lower back tattoos are often oblong in shape, following the slope of the back on either side of the woman's spine. Worn almost exclusively by women, the lower back tattoo functions as body decoration, while underlining sexual attractiveness. Generally, a lower back design will be shaped to accentuate the shape of the female figure. The placement of such tattoos on the lower back may be seen as more sensuous than other common female tattoos (such as the ankle or shoulderblade), as it tends to seduce and sedate onlookers.

There are several attributes of lower back tattoos that have made them popular. While the lower back is not the widest area of the human back, it has abundant space for a large design, and horizontal tattoo designs can be worked easily. Another advantage is that the lower back is less likely to stretch and distort due to minor weight fluctuations, thus avoiding the tattoo's shape becoming warped. In addition, they can easily be concealed under business attire for formal settings.

Lower Back tattoos are also often displayed in conjunction with stylish halfshirts and bellyshirts (also called crop tops) designed to expose the midriff, and low-rise jeans that are slung low around the hips (a fashion style referred to as "Muffin tops").

In Episode 18, Season 29, of the popular comedy show, Saturday Night Live, a skit was aired as an commercial parody for a product called Turlington's Lower Back Tattoo Remover.

In a scene of the comedy film, Wedding Crashers, the character Jeremy Grey (Vince Vaughn), exclaims "Tattoo on the lower back... might as well be a bullseye."

In Germany, a lower back tattoo is known as an "Arschgeweih," meaning "ass antlers."

Lower back tattoo by Marshall Lee June 11, 2006

backtating 

when you lacktate out of your anus, or the backside of your body, AKA diarrhea

"oh man, that taco bell left me backtating all night"

backtating by fil-trek slave February 1, 2010