A few days ago this question has been posted on Worldbuilding, asking about a hypothetical solipsistic society. Yes, it is vague and was ultimately considered as POB (primarily opinion-based, i.e., too vague, not narrowed down enough), which I think is debatable, but I do not disagree wholeheartedly, but that is not the point of this question.
The discussion in the comments quickly ended in disagreement about whether the term solipsism is required to be explained by the author.
Now, if this question was posted on Philosophy I'd assume it obvious not having to explain the term, as it is a philosophical term the audience might likely be familiar with and the discussion would probably not have taken this turn. But since it's unlikely the majority of users on Worldbuilding knows the term, is the author required to explain it?
Like other users, I was unfamiliar with it, but a quick Google search shed light on my mind in less than a minute. I personally do not hold the author responsible to fill holes in my general knowledge, even if those require a certain specialization to be well known. If this is the case—as a follow-up question—how badly established and hard to find it explained does a term need to be before an author should include a rough explanation to a technical term for an audience outside of the specialized field of knowledge?