The string refers to a specific firmware image for the FortiGate VM64 virtual appliance running on KVM (Kernel-based Virtual Machine). Image Details
Releasing build 1262 in the v7.2 branch places this image in a specific stage of Fortinet's development lifecycle. fgtvm64kvmv723fbuild1262fortinetoutkvmqcow2 upd
upd tag might indicate it’s an incremental update image, not a full installer.