A technique where chakra kneaded inside the body is converted into fire, and expelled from the mouth either as a massive orb of roaring flame or as a continuous flame-thrower. The scope of the attack is altered by controlling the volume of chakra that is mustered. The released flames will engulf their target, and leave a crater on the ground's surface. This technique apparently requires more than average chakra reserves and most genin should not be able to do this technique.
According to Kakashi Hatake, this technique was originally created by the Uchiha clan, becoming one of their favoured moves at which they became very adept.
The manga portrays use of this technique as unique to the Uchiha clan while the anime has portrayed it as a common Fire Release technique used by multiple users without any known connection to the Uchiha clan.