Single Point of Failure (SPOF)

 Definition(s):

Any Configuration Item that can cause an Incident when it fails, and for which a Countermeasure has not been implemented. A SPOF may be a person, or a step in a Process or Activity, as well as a Component of the IT Infrastructure. See Failure.

 Source: ITIL

Single Point of Failure (SPOF) is a part of a system that, if it fails, will cause the entire system to stop working. It is a critical element in the system that does not have a backup or redundancy, so if it fails, the whole system is compromised.