With internet connectivity to a premises, the easiest way to provide a degree of internet connectivity redundancy is to install a second circuit to the internet.
If a second circuit is installed and BGP is enabled on it, this is known as BGP multi-homing.
BGP multi-homing is when there are multiple BGP sessions to learn routes and establish connectivity.
BGPs default behaviour is to only present the best path to the routing information base (RIB) or routing table. With only the best path presented, one path is used for a network prefix when forwarding the network traffic to that destination.