Dead zone is a void of darkness created by Garlic Jr. to trap his opponents by sucking them onto there and leave them in the darkness forever. whoever goes there, can never come back unless he or she has the power to crack dimension and reality.
One of the antagonist of Dragon Ball Z named Garlic Junior creates a portal to the Dead zone when he gets frustrated on his opponents. He can open the portal only in transformed state because he can't generate the huge amount of power in normal form to open the portal. By powering up from Makyo star, he can do it easily.
In the Dragon Ball Z : Dead Zone movie Garlic Jr. opened the Dead zone when he couldn't beat Goku and Piccolo. Gohan's power knocked Garlic Jr. into the Dead zone instead and trapped him there.
After four years of his trap inside the Dead Zone, he escaped when his power source Makyo Star appeared on the axis of Earth. When he got power from the star, he break through the void and reappeared to succeed his master plan of dominating the Earth. He was failed again that time by Gohan. When Garlic Jr. couldn't beat Gohan, Piccolo and Krillin, he reopened the Dead zone. while Piccolo and Krllin were busy distracting Garlic Jr, Gohan did a huge Masenko attack on the Makyo star, blowing it up. As Garlic Jr's power source is gone, he reverted back to normal and thus to powerless he was sucked by his own Dead Zone and will be trapped in there for the rest of eternity.
In game, Super Garlic Jr. opens the Dead Zone and throws it like an explosive on his opponent. It vanishes after a few second with a small explosion by inflecting a great amount of damage. Garlic Junior uses Dead Zone as a technique in these following games: