A bolide (French from the Greek βολίς bolis, "missile" or "to flash") is an extremely bright meteor, especially one that explodes in the atmosphere. In astronomy, it refers to a fireball approximately as bright as the full moon, and it is generally considered a synonym of a fireball. In geology a bolide is a very large impactor.
One definition describes a bolide as a fireball reaching an apparent magnitude of −14 or brighter, which is more than twice as bright as the full moon. Another definition describes a bolide as any generic large crater-forming impacting body whose composition (for example, whether it is a rocky or metallic asteroid, or an icy comet) is unknown.
The IAU has no official definition of "bolide", and generally considers the term synonymous with fireball, a brighter-than-usual meteor. However, the term generally applies to fireballs reaching an apparent magnitude −14 or brighter. Astronomers tend to use bolide to identify an exceptionally bright fireball, particularly one that explodes (sometimes called a detonating fireball). It may also be used to mean a fireball that is audible.
Geologists use the term bolide in a somewhat different context than astronomers do. In geology, it indicates a very large impactor. For example, the Woods Hole Coastal and Marine Science Center of the USGS uses bolide as a generic term that describes any large crater-forming impacting body of which its origin and composition is unknown, as, for example, whether it was a stony or metallic asteroid, or a less dense, icy comet made of volatiles, such as water, ammonia and methane.