This question: Where did Horace Walpole get the adjective "Gothic" to describe The Castle of Otranto? which I asked last night has been closed (although I cannot see by whom). Apart from a complaint in a comment that this might be off topic, since it is about terminology, I cannot see any cognizable reason why it would be closed.
“Gothic” fiction is an important genre with major (but not perfect) overlap with fantasy and horror. The Castle of Otranto, the subject of the question, is certainly fantasy. So this is a question about terminology that is closely related to the fantasy genre.
Moreover, even if “Gothic” fiction in general is considered off topic, this question cannot be, since it is a question about a specific (and influential) work of fantasy fiction. The thrust of the question is, What did the subtitle of The Castle of Otranto mean? It is well established that all aspects of on-topic works are on topic for this site (see here: How should we handle questions that are about non-SF/F elements in a SF/F work?). Moreover, this meta question: Is it reasonable to ask about the meaning of phrases in a science-fiction work? shows strong consensus that asking about specific language used in fantasy or science fiction work is on topic. And that is exactly the nature of my question, asking about what the subtitle means.