An evacuated glass bulb containing a metal filament which is heated by electrical resistance to produce light.
(by extension) An article that resembles such a bulb and converts electricity to light by any process.
a fluorescent light bulb
Used in reference to the sudden arrival of a realization, an inspiration, an idea, or the like.
a light bulb moment
An uninvited third person joining a couple's date who prevents or hinders romantic interactions.