Smoke is a collection of airborne
solid and
liquid particulates and
gases emitted when a material undergoes
combustion or
pyrolysis, together with the quantity of air that is
entrained or otherwise mixed into the mass. It is commonly an unwanted
by-product of fires (including
stoves,
candles,
oil lamps, and
fireplaces), but may also be used for
pest control (
fumigation), communication (
smoke signals), defensive and offensive capabilities in the military (
smoke-screen),
cooking, or
smoking (
tobacco,
cannabis, etc.). Smoke is used in rituals where incense, sage, or resin is burned to produce a smell for spiritual purposes. Smoke is sometimes used as a flavoring agent, and preservative for various foodstuffs. Smoke is also a component of
internal combustion engine exhaust gas, particularly
diesel exhaust.