Here’s a sketch of Lulu and her Sugarstar Meteor Rain skill.

For 6 AP, it deals 1–2 damage to every enemy on the board. They don’t need to be grouped together, and your own units won’t be hit.

That’s what the little board beside her illustrates: enemies scattered across different tiles, with allies standing between them. You can soften up several enemies at once, or finish off weakened ones without moving your team out of the way.