What does it mean when something is on backorder?

I recently ordered an iPhone 5 and its on backorder. How long is my wait. I ordered it this past Saturday which was November 3rd. How long will my wait be?

Back-order means it was out of stock at the store, and they had to order more.
Nearly all stores can tell you how long it will be before you get your order. Call
and ask them. Wal-mart lets you track your order online, as do a lot of other
chains.