It means that you have the opportunity to order the product by way of 'back-ordering'. This occurs when the distributor is waiting on the manufacturer to finish producing the next wave of production for that item. There is no way of knowing the exact date, however the manufacturers are generally swift when it comes to fulfilling back-orders. All back orders will be fulfilled. Customers can request a refund at anytime on back-orders. The refund will be issued to the payment source used during the original order.
In other words, the manufacturers issue a first wave of production on items to get a feel for the market demand. Back-orders tell the manufacturer to make and/or ship out more of that product. Most of the time they have a reserve surplus that they send out upon request. However, sometimes they have to manufacture a second wave to keep up with the consumer demand. It is rare that they do not fulfill back-orders. So, you can buy with confidence that you will receive the product as soon as the manufacturer ships out the order.
We do our best to update the website. However, with thousands of products we may not get to update an item as 'in stock' prior to your viewing. Therefore, there's a potential that we have the product you're seeking in transit already.
Once an item is "sold out" we will remove it from the website. "Sold out" to us means that the manufacturer as produced and distributed all of that product and will not manufacture anymore. Consequently, if a product page says "Temporarily Out of Stock" Reality Check expects to have the back-order requests fulfilled.