A strange phenomenon that happens when the power company has a failure in the distribution of power. The lights go out, but the computers stay on thanks to the wonderful UPS.

Power failures happen for various reasons. Sometimes a tree falls on a power line resulting in a few city blocks going out. Other times an overloaded transformer decides to explode, causing power to go out for a few hours because transformer-replacing takes time. Still other times, demand for electricity is so high that the power company is forced to rotate power failures through its grid in order to prevent overloading of its generators. You people in the San Francisco Bay Area probably know what I'm talking about.