Backorders don’t take place if a domain name expires at a registrar that has an auction partner, unless no bids are placed at that auction partner prior to the expiration date. Backorders (when domains are “caught”) only happen when a domain name goes through the full lifecycle and expires, is removed from the registry’s database, and becomes available for new registration.
Thousands of domain names expire every day. The reasons are different. Some owners forgot to renew the domains, some just don't want them anymore or they moved on to other projects. For most people these so called Expired Domains don't have any value. They just see a bunch of Domain Names someone else deleted and move on, but for the people who know about SEO or the value of good Backlinks, Expired Domain Names are money just waiting to get picked up from the street. The only problem is to separate the good ones from the bad ones. That is where comes into play.