Failover is switching to a redundant or standby computer server, system, hardware component or network upon the failure or abnormal termination of the previously active application, server, system, hardware component, or network in a computer network. Wikipedia

automatic switching to a standby computer system or component upon the failure of a previously active system or component Wikidata

An automatic switch to a secondary system on failure of the primary system, such as a means for ensuring high availability of some critical resource (such as a computer system), involving a parallel backup system which is kept running at all times so that, upon detected failure of the primary system, processing can be automatically shifted over to the backup. Wiktionary