From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Scatter Shot (連続 閃光弾, Renzoku Senkōdan; Literally meaning "Continuous Flash Bullet") is an energy wave barrage first used by Piccolo Jr.. First, Piccolo swings his arms apart and charges a purple energy sphere in each hand. He then yells, "Scatter Shot!" as he fires multiple purple energy waves at the opponent, inflicting a huge amount of damage.
Piccolo first used this attack during the battle against Dr. Wheelo in Dragon Ball Z: The World's Strongest. When Goku knocked down Dr. Wheelo with his Power Pole, Piccolo retaliated by blasting the evil robotic scientist with the Scatter Shot. However, Dr. Wheelo was undamaged by the double team attack and headbutted Piccolo into the ceiling.
Piccolo later used this attack during his battle with Freeza after fusing with Nail. After getting knocked into the ground by Freeza, Piccolo removed his weighted clothing and powered up to fight Frieza. Frieza was at first unimpressed, but was soon overpowered by Piccolo's strength and knocked deep into the ground. Piccolo then blasted Freeza with the Scatter Shot, creating a huge explosion. However, Frieza managed to survive and continued the battle with Piccolo.
Scatter Shot is used in the Budokai video game series as Piccolo's ultimate attack under the name Hellzone Grenade.
It is also used in Dragon Ball Z: Attack of the Saiyans. Piccolo sends the enemy into the air and uses the Scatter Shot to form a cirlce around the opponent. He then controls the Scatter Shot to launch towards the enemy, causing it to explode. It is also called Hellzone Grenade.