| 1. | fine particles of ash of a solid fuel carried out of the flue of a furnace with the waste gases produced during combustion. |
| 2. | such ash recovered from the waste gases, used chiefly as a reinforcing agent in the manufacture of bricks, concrete, etc. |
| fly ash n. Fine particulate ash sent up by the combustion of a solid fuel, such as coal, and discharged as an airborne emission or recovered as a byproduct for various commercial uses. |