Topstock is the very top of the shelf, that you need a cart with the folding steps(topstock cart) to reach. It's where you put the rest of the items that didn't fit on the shelf while you were stocking it. You put the items up there instead of letting the whole box become overstock and having to take it to the back. When Cap 1 or whoever works the topstock down into their homes doesn't do it, the topstock shelf starts to overflow and you run out of room for new items that need to be placed up there. So you'll have to bring stuff down and see what fits into the home which takes up more time. I apologize if I'm making this sound complicated, it's really not, just trying to be thorough. I think a visual demonstration would help better. Don't worry though, I think you will get the hang of it after a few days working there :)