Definition of "failover"

failover

noun
countable and uncountable, plural failovers
1. (computing, countable) 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.
  Quotations
  Horizontal scaling gives you some failover and flexibility that you normally cannot get with only vertical scaling.
  2004, Gregory Nyberg, Robert Patrick, Paul Bauerschmidt, Mastering BEA WebLogic Server: Best Practices for Building and ..., page 638
  while Tungsten is not heavily redundant as these systems, the ability of Lustre to support some failover can be leveraged to eliminate single points of failure.
  2005, Proceedings, IEEE Computer Society, page 338
  you have to make sure you can access it or ensure it can provide some failover," says Tarzey.
  2007 July 11, “Business continuity for SMEs”, in Computer Weekly