What characterizes cupping in roofing boards?

Cupping in roofing boards is specifically characterized by the edges of the boards curling up, creating a concave shape. This deformation is typically a reaction to changes in moisture content within the wood. When the edges of the boards absorb moisture and swell, the center of the board can remain relatively unaffected, leading to the characteristic upward curling at the edges. This phenomenon can compromise the integrity of the roofing system, potentially allowing for water infiltration and other issues if not addressed. While the other options mention various changes in the boards, they do not correctly describe the unique visual and structural impact of cupping.