I admit, I didn't know about that screen until now
Maybe item tier. You know, how in some games, usually with random generation of items, there are common/unusual/rare/legendary/etc items.
Or it may represent the chance to find an item without numbers. White is common, green is rare, red is very rare.
We could show a small item icon and its name, or even only icon with name being visible in a tooltip when you select the icon (if it's simple to make). Slots are excessive information. Chances could be shown via stars colors. Like white 80-100% blue 60-80 green 40-60 yellow 20-40 red 1-20% violet<1%
And we shouldn't show enemies elements. We have the bestiary for that already, no need to show it everywhere.