Gunpowder is a substance which burns very rapidly and is used as a propellant in firearms. There are two types:

• Black powder—invented by the Chinese foundation in the 9th Century—was the only widely-known and used practical explosive until the 18th Century. However, it is now primarily only used for fireworks, model rocket engines and in reproduction weapons.
• Smokeless powder replaced black powder as a propellant at the end of the 19th Century and is used in all modern guns.

Both forms of gunpowder burn, producing a subsonic deflagration wave rather than the supersonic detonation wave which high explosives would produce. This reduces peak pressures in a gun, but makes it less suitable for shattering rock or fortifications. However, black powder was, for a few centuries, the only blasting agent available.

Although historically gunpowder has meant black powder, as in the Gunpowder plot, modern references usually imply smokeless powder when referring to the propellant in small arms.