In publishing, where the term originated, an art director organizes the pages of a magazine or newspaper and in consultation with an editor, chooses or designs accompanying pictures or graphics.
Typically, this art director reports to the editor. At larger books or magazines, there are assistant and associate art directors that report to the art director.
Art directors in advertising aren’t necessarily the head of an art department although the title may suggest it. In modern advertising practice, they typically work in tandem with a copywriter.
Together, the art director and copywriter work on a concept for commercials, print advertisements, and any other advertising medium.