For a newbie in the domain name market there are many unknown facts. One of them is what is actually a domain name and what is the web site. A web site is the content you will see when you go to a designated domain name. Domain name in itself is just a name, a designation of the web site. Both are interconnected but are treated separately. Once you buy your domain name this is not the same as to buy a web site. You need to buy hosting or use free hosting then point your domain name to that hosting to actually have a web site presence.
So domain name is like a registration on an automobile. In fact it is just the same, once registered you can drive your do-it-yourself car with that plates. However this is where the differences start, domain name in itself is also a brand for your web site, a portal to it if you wish. So when you buy a domain name you would want to look for a good recognizable, easy to pronounce domain name.
That out of the way, let us talk about back order a bit. You do know that you can use services like GoDaddy to buy yourself a domain name. But what if that domain name is already taken? You can try to negotiate a price with the current owner or you can wait until the name becomes available again. Perhaps current owner has no intention of keeping the name (which is true almost 80% the cases). Then you are in the back ordering game. Companies like Vastus Domains provide backorder services to end customers. In the nutshell the backorder service is a way to purchase your domain name but pay it only when it becomes available. If it never becomes available or it has been purchased by some other company you lose nothing because no money has changed hands. Once the company secures your domain name it will create sales agreement to transfer the ownership and that is when you pay for the domain name.
Beware of the shady business practices for taking your credit card details or money before they actually secure your domain name.