When a domain expires, there's a time period of a little over 2 months when it is not active, but could still be renewed by its current owner. During this time period, the domain cannot be taken by anybody else, but in case it's not renewed, it gets into the so-called Pending Deletion period that lasts 5 days. This is the time when ICANN-accredited registrar firms accept backorders for these domains. In case a specific name is backordered, the registrar will make an attempt to register it for the customer right after it is deleted and available to the public, which gives people the option to obtain a short and memorable domain which may have been employed by somebody else up to now. In the event that the domain is really attractive, a couple of companies may try to register it in the same time and due to the fact that this happens on a first-come, first-serve basis, there is no guarantee that a particular person will get that domain name. However, using a backorder service will give you a much better chance to acquire a specific domain than when you attempt to register it yourself.