Ground Fault Circuit Interrupter
I know how we all hate these things when musicians have broken gear they refuse to fix, even though they had the same broken shit that tripped GFIs last time you had them four months ago, and they know you remember it ... but IMO GFCI should be required for stage power. I just wish everyone else agreed with me so I didn't seem like the crazy one! Crazy is risking your life by handling some guitar rig that looks like, and probably did, just fall off a truck and produces that burning smell when powered on, instead of having a safety device that inconveniences people by making them repair their broke-ass gear. $0.02.