What feature of weather conditions does the term 'ceiling' specifically refer to?

The term 'ceiling' in meteorology specifically refers to the height of the lowest layer of clouds above the ground. This measurement is crucial for pilots and meteorologists as it indicates how much of the sky is obscured by clouds and the potential for visual flight rules (VFR) operation. A lower ceiling means that clouds are closer to the ground, which can significantly impact aviation, as lower visibility conditions may restrict flight operations. Understanding the ceiling helps in assessing the weather's impact on flying conditions, making it an essential aspect of weather reporting and forecasting. Other weather features like wind conditions, humidity levels, and temperature variations do not define the ceiling; rather, they contribute to the overall weather picture.