This value, from 1 to 255, sets how much a VRRP (Virtual Router Redundancy Protocol) virtual router's priority is automatically reduced when a tracked interface goes down, and correspondingly increased when that interface comes back up, a mechanism used to trigger automatic failover to a backup router. An administrator tunes this so that losing a critical uplink drops this router's VRRP priority enough to fall below a backup router's priority, causing that backup to take over as master. With the default value of 10, a tracked interface going down reduces this virtual router's priority by 10 points, which needs to be large enough relative to the priority gap with the backup router to actually trigger a failover.