Final answer:
The subject of this question is English. The question asks for the definition of a thick, heavy fog based on provided texts.
Step-by-step explanation:
The subject of this question is English. The question is asking about the definition of a thick, heavy fog mentioned in the provided texts. The texts describe various aspects of fog, including its appearance, effects, and the atmosphere it creates. The fog is portrayed as dense, suffocating, and prevalent in different settings.