A tattoo, or dermal pigmentation, is a mark made by inserting pigment into the skin for decorative or other reasons. Tattoos on humans are a type of decorative body modification, while tattoos on animals are most commonly used for identification or branding.
That is what wikipedia has to say about tattoos. Looks like the defination needs to be modified soon. A recent study suggest that injecting DNA-containing vaccines with a tattoo gun is far more effective than the way human vaccines are now delivered. Visit Yahoo Health for further details. (photo: Dennis Mojado)
The use of tattoo injections, coupled with the ability to rapidly produce large quantities of a vaccine, might prove extraordinarily valuable in a situation such as a threatened terrorist attack, where a sudden need arises for large amounts of an effective vaccine.