The specific string fgtvm64kvmv721fbuild1254fortinetoutkvmqcow2 refers to a FortiGate Next-Generation Firewall (NGFW) virtual machine image. Specifically, it is a v7.2.1 build 1254 image for the KVM/QEMU hypervisor, provided in the .qcow2 format.
Login: The default username is admin with no password (press Enter when prompted). Set IP on Port 1: fgtvm64kvmv721fbuild1254fortinetoutkvmqcow2 work
Thus, the full meaning is: FortiGate VM 64-bit for KVM, version 7.2.1 build 1254 (Fortinet), provided as a QCOW2 image, aiming to make it work. version 7.2.1 build 1254 (Fortinet)
file acts as the boot drive (Drive A), but FortiGate requires a second virtual disk provided as a QCOW2 image