From the Document: "Presidential Policy Directive 21 established national policy on critical infrastructure and resilience in February 2013. The directive defines resilience as the ability to prepare for and adapt to changing conditions and to withstand and recover rapidly from disruptions. Such disruptions include naturally occurring threats or incidents, deliberate attacks, and accidents. This brief draws from recent GAO [Government Accountability Office] reports on natural and human-caused risks to the electricity grid. It also highlights GAO recommendations that had not been implemented as of September 2021."
Government Accountability Office: https://www.gao.gov/