The KVM host is the physical system that runs the KVM guests. The KVM guests can only run inside a KVM host.
Setting up the KVM host environment is not as hard as you think, but there are a many things to consider before beginning the installation. Spending time planning your KVM host before you install it will save you a lot of trouble later on. The KVM host is running on physical hardware. Find out how you want to use your hardware.
The software configuration for the KVM host has to take care of the possible hardware failures that can happen on the physical host. Once this is configured, the KVM guests can rely on the KVM host, to have its hardware properly monitored.