BSL Physics Glossary - bulb - definition
A bulb gives out (emits) light. There are different types of bulb. The filament bulb is used, for example, in a car headlight or for lighting in houses. There are also fluorescent lights which are energy saving. Another type is an LED (light-emitting diode). These are getting more popular now. For example you can see an array of LEDs in brake lights.
Incandescent (filament) Fluorescent (energy saving) LED lamp
(pictures from Wikimedia)