Magic Materialization is a magical ability used to create physical matter out of thin air.
Namekians of the Dragon Clan have the ability to create objects from nothing, and they use it to create everything from houses and furniture, and those who reach genius-class can also use it to create Dragon Balls.
Kami used this to restore Goku's clothes that were wrecked by Piccolo in the 23rd World Martial Arts Tournament. King Piccolo is believed to have used it (off-screen) to create his throne (which somewhat resembles the throne used by Grand Elder Guru later in Dragon Ball Z). Piccolo uses the Magic Materialization several times to create uniforms for himself and Gohan, as well as a few other items. In the Majin Buu Saga, Piccolo creates an hourglass in order to show the time Super Buu has to wait for his fight with the ultimate warrior, Gotenks.
Spike the Devil Man and Dabura use this ability to make weapons: Spike the Devil Man created a trident for his fight with Goku, Dabura created a sword when fighting Gohan and a spear when opposing Majin Buu. Garlic Jr. used this technique to create a throne in Kami's Lookout similar to the one he had in his fortress. Old Kai created a Crystal Ball, a highly useful device to monitor something that happens with another creature.
In Dragonball GT, Ledgic used it to produced two swords and a spear in his fight against Goku. Nuova Shenron uses this technique to make a lens appear in order to perform his Nova Death Ray attack. In the TV special Dragon Ball GT: A Hero's Legacy, Mamba uses this to create a scythe.