What's that word about design elements, how wood should be wood?

I remember HN used to talk about it a lot, sku-something or skeo-something, but it's a rule in design that wooden objects should be wooden or something like that. I used to see this word thrown around in every UX thread but I can't remember what the damn word is. I've tried googling but I'm not having much luck.

I remember this word bring used a lot right before Material came into public view.

If any body knows what I'm talking about, please help me find this word.