Which term describes a structural member that has a nominal thickness of less than or equal to 2 inches?

The term "board" is correctly defined as a structural member that has a nominal thickness of less than or equal to 2 inches. Generally, boards are used in construction for various applications, such as sheathing, flooring, and other structural elements. Their thinner profile distinguishes them from other categories of wood products like dimensional lumber and timber, which have different thickness criteria.

Dimensional lumber typically refers to wood with a thickness greater than 2 inches, often used for framing and structural components. Timber, on the other hand, also implies larger pieces of wood commonly used in heavy construction, usually exceeding the 2-inch thickness. The term "lumber" can refer to all forms of wood used for construction, but without specific dimension qualifiers, it does not directly indicate a thickness of less than or equal to 2 inches. Therefore, "board" stands out as the most precise term for a structural member meeting this size criterion.