Which of the following best describes 'tangential'?

The term 'tangential' is best described as having superficial relevance to a topic or issue. This implies that something tangential is not the main focus and may only connect to the topic in a minor or indirect way. In various contexts, such as discussions or arguments, a tangential point may veer off from the central theme or idea, making it less significant in terms of importance and directly related content.

The other options suggest levels of relevance that are deeper or more direct than what 'tangential' indicates. For example, describing something as of deep relevance or extremely relevant would suggest a strong connection to the main subject, while being highly factual implies a strict adherence to factuality, which does not align with the connotation of being tangential. Thus, 'superficial relevance' accurately captures the essence of the word 'tangential'.