What is Loss of load?

Loss of load in an electrical grid is a term used to describe the situation when the available generation capacity is less than the system load. Multiple probabilistic reliability indices for the generation systems are using loss of load in their definitions, with the more popular being Loss of Load Probability that characterizes a probability of a loss of load occurring within a year. Loss of load events are calculated before the mitigating actions are taken, so a loss of load does not necessarily cause a blackout.