What is defined as a tattoo remover?

The correct answer is a substance for removing tattoo ink. Tattoo removers are specifically formulated products that help break down the pigments used in tattoos, allowing them to fade or be eliminated from the skin. These substances may contain various active ingredients that interact with the ink and the skin, facilitating the removal process.

In the context of the other options, a professional service to remove tattoos pertains to the overall procedure of tattoo removal, which may involve the use of these substances but does not define what a tattoo remover is. Similarly, any ink used for commercial tattoos refers to the material applied to create tattoo art, not to any remover. Lastly, a type of medical device for tattoo application is unrelated to the process of removal, as it focuses on the application of tattoos rather than their removal. Thus, the definition of a tattoo remover is clearly centered on the substances specifically designed for ink removal.