A hypermarket is a single store that is supposed to be a step up from supermarket - in that it covers pretty much everything a grocery and a department store has. Think of it as a Coles and a Kmart next to each other, with the dividing wall knocked down. They are really huge stores.
The only drawback is that their toy sections are pretty pathetic. I never go there to check out their toy stock, because they rarely have any TFs in stock.
Not sure if they are a successful concept though, as the two stores are still operating, but no others have been opened during that 15-20 year period. I had heard rumours that they were going to be reverted to Kmarts or Coles a few years ago when Coles Group was going through a huge restructure (which saw the end of the Bi-Lo brand in most states), but it never happened, so maybe wasn't true.