When a domain name expires, there is a period of a little over sixty days when it is not active, but could still be renewed by the current owner. During this period, the domain cannot be taken by anybody else, but if it's not renewed, it goes into the so-called Pending Deletion period that lasts 5 days. This is when ICANN-accredited registrar firms accept backorders for such domain names. When a specific name is backordered, the registrar will try to register it for the customer as soon as it's deleted and available to the public, which gives people a chance to get a short and easy to remember domain that may have been employed by another person up to now. In the event that the domain is quite attractive, several companies could 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 have that domain. Nevertheless, employing a backorder service will give you a lot better chance to end up getting a particular domain than if you attempt to register it manually.