The dead wall is the last seven stacks (14 tiles total) of the wall. Dead wall tiles are never played except when players declare kongs or flowers and draw a replacement tile (also called supplement or loose tile).
To distinguish the dead wall from the remainder of the “live” wall, the dead wall maybe separated from the rest of the wall so that there is a clear distinction between the two. This will act as visual aide to get a sense of how many tiles are left remaining. The last fourteen tiles will always be considered dead so if tiles are taken as replacement for kongs and flowers the last tiles in “live” wall in turn takes takes its place.
The kong box (or flower box) is variation of the dead wall which isn't replenished when tiles are taken from it. It is the last seven stacks of the wall with the last stack (two tiles) placed them on top of the remaining six as show here. When drawing a replacement for a kong or flower one of these “loose tiles” are taken first.
When both loose tiles are drawn, take the last stack of the kong box to replace the loose tiles on top.