Yeah sorry, I wasn’t really using a true terminology. What I meant was, install planks of nice looking wood (stained/finished to your color choice) around that vertical surface in your pics. Personally, I would have the planks extend about 1/4-1/2 inch above the top of your floor (on 3 sides, but flush at the side where your stairs exit), and then install like a 1/2” (or whatever thickness gets you flush to the top of those vertical planks) by 1.5” or 2” with a nice finished edge to sort of “cap” over your flooring on the upper level. And on the stair exit side, you can pop on that metal piece that the other commenter posted.