When a domain expires, there is a time period of a little over eight weeks when it is not active, but could still be renewed by its current user. During this time period, the domain cannot be taken by anybody else, but in case it is not renewed, it enters the so-called Pending Deletion period that lasts five days. This is when ICANN-accredited registrar companies take backorders for these domain names. If a specific name is backordered, the registrar will make an attempt to register it for the customer right after it's deleted and available to the general public, which gives people an opportunity to obtain a short and easy to remember domain that may have been employed by another person up to now. If the domain is rather appealing, several companies can try to register it in the same time and since this happens on a first-come, first-serve basis, there's no guarantee that a specific person will get that domain. However, employing a backorder service will give you a better chance to obtain a particular domain than if you attempt to register it yourself.