This is the 99th most frequent Serbian word.
облачно
Cloudy.
In this sentence, 'облачно' is used as a predicate adjective to describe the weather condition.
Данас је напољу облачно.
Today it is cloudy outside.
Here, 'облачно' is used as an attributive adjective describing the noun 'време' (weather).
Не волим када је облачно време јер тада нема сунца.
I don't like cloudy weather because there is no sun then.
In this example, 'облачно' is again functioning as a predicate adjective in a subordinate clause explaining the reason.