Ability to maintain capability in the face of adversity" (INCOSE)
Ability to adapt to changing conditions and prepare for, withstand, and rapidly recover from disruption. (DHS 2010)
INCOSE Resilient Systems Working Group.
DHS. 2010. Department of Homeland Security Risk Lexicon," September 2010. Accessed on 11 September 2012. Available at http://www.dhs.gov/xlibrary/assets/dhs_risk_lexicon.pdf.
The above definition is the official definition of the US government. The same definition appears in both sources. Although the government's interest is in the resilience of infrastructure systems, the definition is sufficiently general to apply to any human-made system. The word has been applied in material sciences, ecology, and psychology. However, those definitions do not apply here. Some sources use the word "resiliency," but "resilience" is more common.
SEBoK v. 2.2, released 15 May 2020