Dictionary

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.

Example: a fluorescent light bulb

Used in reference to the sudden arrival of a realization, an inspiration, an idea, or the like.

Example: a light bulb moment

An uninvited third person joining a couple's date who prevents or hinders romantic interactions.