Dragon's breath is a special type of incendiary-effect round for a 12 gauge shotgun. Dragon's breath consists primarily of magnesium pellets/shards. When the round is fired, sparks and flames can shoot out to about 100 ft. Dragons breath is normally chambered in 12 gauge 2 3/4" shot shell. The rounds are safe to fire out of an improved cylinder bore as well as a modified choke barrel, common on many shotguns.
While its actual professional combat or tactical usage remains undocumented, the visual effect it produces is impressive and entertaining, similar to that of a short-ranged flamethrower or fireworks, making it popular among gun enthusiasts in countries where that type of ammo may be purchased by civilians without any restrictions by law, e.g., the United States. Also undocumented, it has been claimed by enthusiasts that the rounds are often used as a distress signal, similar to a very short duration emergency flare gun, though some would argue a flare would be better fitted for such. The round has also been used for intimidation purposes, it may also be used as a less-than-lethal option for self-/home-defense. Compared to most regular types of shotgun ammunition that is mass-produced, the pyrotechnic shell is somewhat expensive, and can cost anywhere between $1-$5 (USD) per shell, depending on caliber and load. There is little or no record of its use in actual combat. Due to the shells being low-pressure charged rounds, it is not suited to be used in an auto-loading shotgun or semi-automatic shotgun; as it does not produce enough recoil energy to cycle the automated-action, causing the mechanism to fail to cycle.
Dragon's breath rounds are banned by law in most countries, due to their inherent fire hazard. Even in areas where the round may be shipped, an extra fee for hazardous materials may be charged. It is heavily implied that Dragon's breath rounds qualify as incendiary weapons in Protocol III in the Convention on Certain Conventional Weapons, and is therefore heavily restricted in usage in the signatory nations 
In popular culture
In the FOX show Bones (season 8, ep. 19), Dr. Jack Hodgins suspects a dragon's breath shell could have caused the death of a former Marine sergeant, and the subsequent fire that destroyed the room around her.
In The Dresden Files, the inhuman assassin Kincaid uses dragon's breath rounds to kill Red Court Vampires.
In the TNT show Falling Skies, Jimmy uses dragon's breath rounds to kill two Skitters while on patrol.