What type of cloud layer does "BKN" represent?

"BKN" stands for "broken clouds," which indicates that the cloud cover consists of 5 to 7 tenths of the sky covered by clouds. In aviation weather observation, this term is used to describe a situation where there are significant gaps of clear sky visible among the clouds, but the overall condition is more than just a few clouds. This is why it is referred to as "partially broken" because while there is considerable cloud cover, it is not entirely overcast. The presence of broken clouds can have implications for visibility and flight conditions, making it an important term for pilots and meteorologists alike to understand.

The other options describe different states of cloud cover that do not align with the definition of "BKN." For example, completely covered cloud cover would signify an overcast condition (which would be represented as "OVC"), few clouds indicates minimal cloud cover (commonly referred to as "FEW"), and clear sky indicates no significant cloud cover at all. Each of these terms has its own specific meaning in weather observation, further emphasizing how "BKN" represents a unique condition of partially broken cloud layers.