Virtual Router Redundancy Protocol (VRRP) mitigates single point of failure risk for routers providing access to and from local area networks (LAN). If a LAN is statically routed through a single router, failure of that router disconnects the LAN from wider networks. Under VRRP, multiple parallel routers can be configured to provide such access. One of these routers is designated as the master. If the master fails, a backup router is elected as the new master. Routers using VRRP form a virtual router group, advertising a single shared default gateway address for client configuration. VRRP is a technique for improving network availability.
See: RFC 5798
References:
http://www.cisco.com/en/US/docs/ios/12_0st/12_0st18/feature/guide/st_vrrpx.html
http://www.juniper.net/techpubs/software/erx/junose53/swconfig-routing-vol1/html/vrrp-config4.html