A default route is used to direct packets destined for a network that is not listed in the routing table. It is often referred to as the 'gateway of last resort' because it is the route used when no other route matches the destination IP address. This is essential for ensuring that packets have a path to follow even when their destination is not known, thus maintaining the flow of traffic on the network. Specifying a direct route requires an explicit network destination and is not suitable for handling all unknown destinations. Routing information protocols are designed for exchanging routing table information. Administrative distance is a concept used to rate the trustworthiness of a specific route when multiple routes to the same destination exist.