1. A variety of "power glitch" (see glitch); momentary zero voltage on the electrical mains.
2. Missing characters in typed input due to software malfunction or system overload (one cause of such behaviour under Unix when a bad connection to a modem swamps the processor with spurious character interrupts; see screaming tty).
3. Mental glitches; used as a way of describing those occasions when the mind just seems to shut down for a couple of beats. See glitch, fried.