The best vocabulary word to describe the artwork depends on its characteristics. However, if the artwork features shapes and structures that are more free-flowing and resemble natural forms, "organic form" would be the most appropriate choice. If it consists of angles and regular shapes, "geometric form" would fit better. If it emphasizes the outline or contour, "line" would apply. If the artwork highlights the lightness or darkness of colors, then "value" would be suitable.
To determine the best answer, consider the specific features of the artwork in question. If you provide me with more details about the artwork, I can help you choose the most fitting term!