What are expired / deleted domains?
A special category of domains for sale are called "expired and deleted" domains. These are domains the previous owner failed to renew, either willingly or not. In this case, the registrar will try to auction off the domain right before the end of the yearly registration cycle. This is called "expired" domain. If the registrar fails to sell the domain, it will then revert to the pool of freely available domains. Services like SnapNames and Pool specialize in buying these domain as soon as they expired. These services auction off domains in anticipation of their deletion. These auctions (or pre-ordering to be exact) are called "Pending Delete" domains.