以下内容摘自Libvert terminology and goals：
a node is a single physical machine
an hypervisor is a layer of software allowing to virtualize a node in a set of virtual machines with possibly different configurations than the node itself
a domain is an instance of an operating system (or subsystem in the case of container virtualization) running on a virtualized machine provided by the hypervisor Hypervisor and domains running on a node
Now we can define the goal of libvirt: to provide a common and stable layer sufficient to securely manage domains on a node, possibly remote.
在libvirt中，node即指物理机器，domain可以理解为虚拟机。