Scripts

I can't figure out this script. I need a fireball animation on the world map. I found it in the Nival campaign. It seems like I understand it now, but what is "boom"?
Here is the script: PlayVisualEffect( FIREBALL, '', 'boom', x, y, 0, 0, GROUND );

Play3DSound( "/Sounds/_(Sound)/SFX/FireballHitMono.xdb#xpointer(/Sound)", x, y, 0);