The queue is used to manage the checkout process in times of high demand. When you try to purchase an item during a period of high demand, you may be placed into a queue. The queue will save your spot in line until it is your turn to checkout. Once you reach the front of the queue, your item will be reserved and you will have 10 minutes to complete your transaction. You are only allowed to be in one queue at a time.
A spot in the queue does not reserve your item. Your item is only reserved once you reach the front of the queue and enter the checkout process. An item can sell out while you are in the queue.