familiar with the term "dado?"
Yes, but I don't run into people using the term here much, I think it's British, they usually call it wainscoting or "the panel below the rail." Dado is also a term used in joinery, meaning to cut a slot, usually with a router or table saw, often used for cabinetry and shelving.
I knew Steve would make that distinction. Very common term for joinery, wainscot Is more common for that lower wall dressing.