Fa'Diel is the name of the world in which at least some of the games of the Mana series take place. It has a rich variety of climates and geographic features not unlike our world. It is inhabited by several intelligent races and is said to have been created by the Mana Goddess. It is usually divided into at least three kingdoms, some of them allied, others at war with each other.
Despite sharing a name, the Fa'Diels featured in each game are entirely different worlds from each other, and thus look completely different. There are two notable pairs that are exceptions to this rule though, as Trials of Mana and Heroes of Mana share the same world, as do Dawn of Mana and Children of Mana.