In astronomy, a fireball is a meteor which is large enough to be apparently brighter than the planet Jupiter. Fireballs frequently leave a trail which can be visible for several minutes, and can sometimes produce a noise loud enough to be audible from the ground during or shortly after the period in which the fireball is observed.
A Primordial Fireball is a term coined by P.J.E. Peebles to describe the universe during its first 300,000 years of existence. The fireball supposedly derived most of its energy from the annihilation of particles and antiparticles during the first second after the Big Bang.
In fantasy role-playing games, "fireball" is a basically a magical grenade created by a spell: a wizard points at the target, casts the spells, and a ball of fire wizzes off at the target, exploding on impact.
Jerry Lee Lewis once described a lover as a fireball, or Great Balls of Fire.