Libvirt is a framework supported by Red Hat to manage virtulization in linux environments. Libvirt is very popular and used by virt-manager, openstack etc. Libvirt sits between user level and kernel level then provides practical api to manage vms. Libivirt supports kvm, vmware, hyperv etc. but developed natively for kvm. Libivrt provides api for remote management.
Node is a host that runs vms on it.
Hypervisor is the kernel level components that provides resources for virtulization.
Domain is the components that consist of vm and other resources.
Volume is single disk that is used by vm
Pool is a list of disks.
Libvirt domain definitions are kept in xml format in /etc/libvirt/… The definition consist of classic qemu parameters and some extra parameters.