Commonly used in microcontrollers to describe supply voltage dropping below threshold. It could cause RAM corruption, erratic behaviors of robots, overshoot in voltage regulators, battery fluid leaks etc., and so optional detection features are often made available to reset or stop the processor and notify the application on next boot.

It's also used in utility power supplies to describe line voltage going below spec. It's considered a dangerous condition in that context too, as lots of non-smart equipment tend to run at higher amperage at lower voltage and/or fail to start/run and catch fire.

1: https://developerhelp.microchip.com/xwiki/bin/view/products/...