a glass bulb, filled with oxygen and aluminum or zirconium wire or foil, which, when ignited electrically, burns with a brilliant flash to provide momentary illumination of a subject.
flash·bulb or flash bulb (flāsh'bŭlb') n. A glass bulb filled with finely shredded aluminum or magnesium foil that is ignited by electricity to produce a short-duration high-intensity light flash for taking photographs. Also called photoflash.