Storm

Storm is a keyword ability on instants and sorceries that creates a copy of the spell for each spell played before it in the current turn.

All tournament-legal cards with Storm were first printed in Scourge.

From the Comprehensive Rules:

• 502.30. Storm
  • 502.30a Storm is a triggered ability that functions while the spell is on the stack. “Storm” means “When you play this spell, put a copy of it onto the stack for each other spell that was played before it this turn. If the spell has any targets, you may choose new targets for any number of the copies.”
  • 502.30b If a spell has multiple instances of storm, each triggers separately.