European Project Definitions
The following definition was used in FORTRESS FP7 , and published by Pescaroli and Alexander (2015) in Planet@Risk, the journal of the Global Risk Forum Davos.
'Cascading effects are the dynamics present in disasters, in which the impact of a physical event or the development of an initial technological or human failure generates a sequence of events in human subsystems that result in physical, social or economic disruption. Thus, an initial impact can trigger other phenomena that lead to consequences with significant magnitudes. Cascading effects are complex and multi-dimensional and evolve constantly over time. They are associated more with the magnitude of vulnerability than with that of hazards. Low-level hazards can generate broad chain effects if vulnerabilities are widespread in the system or not addressed properly in sub-systems. For these reasons, it is possible to isolate the elements of the chain and see them as individual (subsystem) disasters in their own right. In particular, cascading effects can interact with the secondary or intangible effects of disasters.".
The CIPRNet project  uses the following definition:
“A cascading failure occurs when a disruption in one infrastructure causes the failure of a component in a second infrastructure, which subsequently causes a disruption in the second infrastructure.” 
The RESIN project  gives the following definition:
A sequence of events in which each individual event is the cause of the following event; all the events can be traced back to one and the same initial event.
Sequence of events in which each individual event is the cause of the following event; all the events can be traced back to one and the same initial event. 
The uncontrolled successive loss of system elements triggered by an incident at any location. Cascading results in widespread electric service interruption that cannot be restrained from sequentially spreading beyond an area predetermined by studies. 
- ↑ http://fortress-project.eu
- ↑ Pescaroli, G, Alexander DE (2015). A definition of cascading disasters and cascading effects: Going beyond the “toppling dominos” metaphor. Planet@Risk, Global Forum Davos, 3(1): 58-67
- ↑ http://www.ciprnet.eu/
- ↑ Rinaldi, S., J. Peerenboom, and T. Kelly (2001). Identifying, understanding and analysing critical infrastructure interdependencies. IEEE Control Systems Magazine, pp. 11–25.
- ↑ http://www.resin-cities.eu/
- ↑ Rome, E., Voss, N., Connelly, A., Carter, J.G., Handley, J.F. 2015. Urban critical infrastructure systems., State of the art report 1, The Resin Project.
- ↑ Protection of Critical Infrastructures – Baseline Protection Concept: Recommendation for Companies, BMI.
- ↑ Glossary of Terms Used in NERC Reliability Standards, Updated May 8, 2014