See Resume Guest
Suspension is a way to immediately “pause” a guest so that it no longer uses the CPU, disk, or network.
However, it will continue to reside in memory.
NOTE: An alternative to Suspension is to save/load a session instead, which would mean it no longer takes up memory, but can be restored to its exact state (even after a reboot).
See: Save Guest and Restore Guest
WARNING: A suspended session will be lost if the host system is rebooted.
However, a saved guest does persist.
virsh suspend VM_ID_OR_NAME