Volt Tackle is Pikachu's Final Smash attack in SSBB. When Pikachu uses this attack, he temporarily turns into a gigantic ball of light. The ball of light will then fly around the stage at great speeds, and the direction Pikachu goes during this move can be controlled by the player.
Volt Tackle is named after a secret move in more recent Pokemon games that only members of the Pikachu family can learn.