A Fire Flower is one of the many Power Ups you can find in the Mario games. The Fire Flower gives you the ability to throw bouncing fireballs at the enemy.
In Super Mario World (albeit in a different shape) and New Super Mario Bros., when used against nearly any foe, they turn to coins.
In Super Mario Galaxy it not only allows the player to damage enemies with fire balls, but also light torches and break wooden crates.
In Super Smash Bros. and Super Smash Bros. Melee(and possibly Super Smash Bros. Brawl), it sets loose a defense-eating flame; nothing like the fireballs from the Super Mario Series.