Terra is a small planet floating about in space in the Final Fantasy IX universe. In the game, it is home to purely genomes, groups of soulless golems whose purpose is to be the vassals for which the souls of Terra may return. Their leader, Garland, is a mysterious and powerful man, created by the souls of Terra to watch over their plan to obtain souls from Gaia and to eventually bring them all back to life.
It is explained by Garland to Zidane that he and Kuja were Angels of Death, intended to cause as much chaos and death as they could to create an influx of souls through the Iifa Tree to return to Terra. With the souls returning to Terra, the souls of the former Terran people would be able to live yet again, in the bodies of the Genomes. Zidane didn't wind up carrying out his destiny, and instead became the person we saw in the game. Because of this, he refused to let Terra complete it's absorption of Gaia, and together with the party, he challenged Garland, and ultimately, Kuja.
There are two locations in Terra: the city of Bran Bal (home of the Genomes) and Pandemonium, a large, dungeon-like place, full of many mysteries and where Garland resides. In Bran Bal, Zidane discovers who he really is: a genome, a soulless entity whose sole purpose is to house the souls of Terrans. He goes on a depressive bend in Pandemonium, losing his humanity and general personality, until coming to thanks to his friends.
Terra is home to Zidane, but also Kuja and his powerful airship the Invincible. Kuja was Terra's first Angel of Death, until Zidane was created to replace him. He cast Zidane down to Gaia, intending to kill him, and went on a warpath of destruction since learning of his mortality. When the party confronts him on Terra, he ascends to Trance form, and with his immense new powers, he destroys his entire home planet.
*It should be noted that all three bosses are fought one right after another, no free time in between.
Items: Ether, Elixir, Dragon Mail, Kaiser Knuckles
Items: Battle Boots, Ninja Gear, Dark Gear
Items: Ether, Carabini Mail, Light Robe