This question already has an answer here:
Below is the question and the answer is "what."
Xerosis is a technical medical term for ___ most people refer to as dry skin.
From my instinct, I understood why "what" should be an answer. The problem is I can't explain why "which" can't be an answer.
If I chose "which" for this question, then "which" indicated the word "term," but it couldn't be like that. I need an explanation based on grammar.