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 the fictional Super Mario Brothers realm, a fireball is a weapon used by Mario and Luigi to defeat their enemies.
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.