A short-barreled, breech-loading signal pistol which can also be used as a weapon. It launches its projectile in an arc, and can be used for long-range indirect fire when aimed outside of V.A.T.S. After damage caused by the initial hit, affected targets will take additional fire damage for a short time.
The flare gun also has the ability to frighten abomination-type creatures. Whilst on fire, they will attempt to flee from the player, but will resume their normal behavior once extinguished. Note also that a fleeing creature may run right at and past the player if there is no other line of escape, but will not attack while on fire.
The object effect is named "Burninate All the Peoples", a reference to Strong Bad's Trogdor song in Homestar Runner.
A flare gun is a real tool used in many careers, such as many law enforcement careers, and in some military installations. It is used mostly as a warning sign, or a sign for help, despite its in-game use as a weapon.