What principle of design refers to the variation of elements in a printed product?

The principle of design that refers to the variation of elements in a printed product is contrast. Contrast involves the differentiation between elements, including colors, shapes, sizes, and textures, which helps to create visual interest and guide the viewer's eye. This variation is essential in design as it helps to communicate a message effectively and can emphasize important information or elements within the composition.

When contrast is used thoughtfully, it can enhance readability, create focal points, and establish a hierarchy of information, making the design more engaging and dynamic. For instance, contrasting colors can help elements stand out, while contrasting sizes can indicate the importance of different pieces of content. This principle is foundational in creating effective visual communication in advertising design and other graphic design fields.