Fencing is the ability to make a node unable to run resources, even when that node is unresponsive to cluster commands.
Fencing is also known as STONITH, an acronym for "Shoot The Other Node In The Head", since the most common fencing method is cutting power to the node. Another method is "fabric fencing", cutting the node’s access to some capability required to run resources (such as network access or a shared disk).
