A tattoo machine is a hand-held device generally used to create a tattoo

Tattoo

A tattoo is made by inserting indelible ink into the dermis layer of the skin to change the pigment. Tattoos on humans are a type of body modification, and tattoos on other animals are most commonly used for identification purposes...

, a permanent marking of the skin

Skin

-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

 with indelible ink

Ink

Ink is a liquid or paste that contains pigments and/or dyes and is used to color a surface to produce an image, text, or design. Ink is used for drawing and/or writing with a pen, brush, or quill...

. Modern tattoo machines use electromagnetic coils to move an armature bar up and down, Connected to said armature bar is a barred needle grouping that pushes ink into the skin. Tattoo artists generally use the term "machine", or even "iron", to refer to their equipment. The word "gun" is often used but is looked down upon by professional artists.
The predecessor to the tattoo machine was the electric pen

Electric pen

Thomas Edison's electric pen, part of a complete outfit for duplicating handwritten documents and drawings, was the first relatively safe electric motor driven office appliance produced and sold in the United States.- Development :...

 invented by Thomas Alva Edison and patented under the title Stencil-Pens in Newark, New Jersey, United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 in 1876.