From Minecraft Wiki
Fireball may refer to:
Ghast fireball - a projectile fired by ghasts that explodes upon contact with a block or mob. It can be deflected. The impact will cause projectile damage, and the ensuing explosion will cause blast damage.
Blaze fireball - a projectile fired by blazes that ignite mobs and blocks upon contact. It cannot be deflected. The impact will cause projectile damage, and the fires will cause fire damage.
Fire charge - a craftable item designed to be shot from dispensers. Once fired, it becomes the same projectile as a blaze fireball.
Ender charge - a projectile fired by ender dragons that emits harmful purple clouds upon impact. It cannot be deflected. The fireball itself deals no damage, but the cloud it leaves deals Harming damage.