A flash (also known as a tattoo flash) is a design or picture that is used in order to create a tattoo. They often come in sets like a poster (called flash sheets), and can be seen in most tattoo shops.
Tattoo flashes are often drawn for general use, rather than being a custom made piece like some personal tattoos. However, some flashes have space for personalisation, for example space for the person to include a name in their tattoo.
Tattoo flashes come in a variety of different designs, and are divided into categories such as celtic, heart, arm band tattoos e.t.c. A person wanting a tattoo made from a flash chooses which design they like best. Then the tattooist uses a stencil to draw the basic design onto the skin of the person being tattooed, and afterwards starts to make the tattoo.