A "rough sea" refers to ocean conditions characterized by large waves, strong winds, and turbulent waters. These conditions can make navigation difficult for ships and boats, leading to potential hazards for sailors. The height of the waves and the intensity of the wind can vary, but generally, a rough sea is associated with stormy weather. Rough seas are often caused by weather systems such as storms or hurricanes, which generate powerful winds that disturb the water's surface. This can result in waves that are several feet high, creating a challenging environment for maritime activities. Safety measures are crucial during such conditions to protect both vessels and crew.