What does the term 'visibility' refer to in weather observations?

The term 'visibility' in weather observations specifically refers to the distance one can clearly see. This measurement is essential for various activities, such as aviation, driving, and other outdoor events, as it impacts safety and operational decisions. Visibility can be affected by several factors, including weather conditions like fog, precipitation, or smoke, all of which can reduce the distance at which objects can be seen clearly.

In contrast, the other options focus on different meteorological concepts. The altitude at which clouds form relates to cloud base height, the amount of moisture in the air is described by relative humidity or dew point, and the speed of the wind indicates how fast air is moving in a specific direction. Each of these concepts is crucial for understanding weather conditions, but they do not pertain directly to what visibility measures.