# Review of Power System Resilience Concept, Assessment, and Enhancement Measures
## 3 Understanding Power System Resilience  
### Definition of Resilience  
With the occurrence of extreme events becoming more frequent, there has been an increase in large-scale power system disruptions, greatly impacting the integrity of the grid. In addition to possessing robustness and reliability, it is crucial for a power system to have resilience in order to minimize the effects of these extreme events [56]. The term \"resilience\" derives from the Latin word \"resilio\", which literally means the ability of an object to return to its original state after being subjected to pressure [57]. In 1973, [PERSON] introduced the concept of resilience in ecosystems, stating that it determines the persistence of relationships within a system and the ability of that system to absorb variables and still function properly [58]. To date, resilience still does not have a standardized definition. The concept is still evolving, expanding, and being applied to various fields. The definitions of resilience by different organizations or associations are as follows:  
* United Kingdom Energy Research Center (UKERC) [59]: Resilience is the ability of an energy system to continue delivering affordable energy services to consumers even in the face of disruptions. When the external environment undergoes changes, a resilient energy system can quickly recover from impacts and provide alternative means to meet energy service needs. * U.S. Department of Energy [60]: Resilience refers to the ability of an energy facility to quickly recover from damage to any of its components or external systems it relies on. Resilience measures do not prevent damage, but rather enable the energy system to continue operating, even in the event of damage or power outages, and quickly restore normal operations. * The National Infrastructure Advisory Council (NIAC) [61]: Infrastructure resilience is the ability to mitigate the magnitude and/or duration of disruptive events. The effectiveness of a resilient infrastructure or enterprise depends on its capability to anticipate, absorb, adapt to, and/or quickly recover from potential disruptive events. * The Presidential Policy Directive (PPD-21) [62]: Resilience involves the capability to prepare for and adapt to changing circumstances, as well as the capability to withstand and recover rapidly from disruptions. Resilience encompasses the ability to withstand and recover from deliberate attacks, accidents, or naturally occurring threats or events. * American Society for Industrial Security (ASIS) [63]: Resilience refers to an organization's ability to adapt to complex and ever-changing environments. It is the capability of an organization to resist the impact of events or to recover to an acceptable level within an acceptable timeframe after being affected by such events. Resilience is the ability of a system to maintain its functionality and structure in the face of internal and external changes, and gracefully degrade if necessary. * The United Nations-International Strategy for Disaster Reduction (UN-ISDR) [64]: Resilience refers to the ability of a system, community, or society that may potentially face hazards to adapt and achieve and maintain an acceptable level of functioning and structure by resisting or changing. This depends on the inherent ability of social systems to enhance their capability to learn from past disasters, thus better protecting the future and improving risk reduction measures. In contrast, [PERSON] et al. [65] simply define resilience as \"the ability of systems to recover from adversity\". In reality, the specific definition of resilience is not as important as its fundamental concepts. Nearly all definitions share three common concepts: 1. The system is able to absorb potential disruptions. 2. The system is capable of adapting to these disruptions. 3. The ability to recover rapidly from disruptions [6; 66]. In other words, the system must possess the abilities of absorption, adaptation, and recovery. [PERSON] et al.