What is the definition of a ceiling in aviation terms?

In aviation terms, the correct definition of a ceiling refers to the lowest cloud layer that is reported as broken or overcast. This definition is essential for pilots and air traffic controllers, as it indicates the minimum altitude where visibility is affected due to cloud cover. A broken layer is defined as having between 5/8 and 7/8 of the sky covered with clouds, while an overcast layer means the entire sky is covered. Understanding this definition helps in decision-making during flight operations, particularly for approaches, landings, and maintaining visual flight rules (VFR) or instrument flight rules (IFR).

The other options, while they refer to aspects related to clouds or visibility, do not accurately capture the specific aviation definition of "ceiling." The lowest cloud layer reported as clear does not meet the criteria for a ceiling since it indicates no significant obstruction to visibility. The highest cloud layer visible in the sky is irrelevant to determining the conditions impacting flight safety. Lastly, the average height of all cloud layers does not reflect any operationally useful definition in aviation, as it does not specify visibility limitations critical for pilots.