Why are virtual machines in KVM/QEMU called "domains"?

I noticed when using virsh that VMs are referred to as "domains". Why are they called that instead of "virtual machines"? $ virsh virsh # help ... Domain Monitoring (help keyword 'monitor'): domblkerror Show errors on block devices domblkinfo domain block device size information domblklist list all domain blocks domblkstat get device block stats for a domain domcontrol domain control interface state domif-getlink get link state of a virtual interface domifaddr Get network interfaces' addresses for a running domain domiflist list all domain virtual interfaces domifstat get network interface stats for a domain dominfo domain information dommemstat get memory statistics for a domain domstate domain state domstats get statistics about one or multiple domains domtime domain time list list domains ... virsh # list --all Id Name State ---------------------------------------------------- - centos_vagrant_test_test_vm shut off - collectd01 shut off - grafana01 shut off - influxdb01 shut off - JobDBWin7_Stable shut off - OpenWRT_Red shut off