What do we call the portion of a composition that a designer leaves for the printer to trim off?

The correct choice is "C. Bleed." In graphic design, bleed refers to the area of a design that extends beyond the actual dimensions of the final printed piece. This extra space ensures that when the item is trimmed to its final size, there are no white edges or gaps. By incorporating bleed, designers can create a seamless look where colors and images reach the very edge of the finished product.

Using bleed is especially important in printing because it accommodates slight variations in cutting. If a design lacks bleed and the cutting is even slightly off, it could lead to unintentional white borders surrounding the design. Thus, including bleed is fundamental in ensuring that the printed material maintains visual integrity and professionalism.

The other terms mentioned have distinct meanings that do not directly relate to the area left for trimming. For instance, a margin refers to the space between the content and the edge of the paper, which serves as a buffer but is not meant to be trimmed. Padding is typically used in digital design to create space within elements, while trim indicates the final size of the printed item rather than the area intended for cutting.