A mysterious fruit that grants superpowers at the expence of the ability to swim in the world of One Piece. They come in three basic types, are typically covered in swirly lines and they all taste awful.
Their powers are unique and only one user of the same power exists at the same time. Eating more than one fruit is considered fatal, thus no one can have more than one power (the only exception being Marshall D Teach for some unknown reason) The fruits "respawn" after the user dies.
Elemental type, allows the user to turn into and control a certain element such as Fire, Smoke or Mud.
Animal type, allows the user to transform into a certain animal as well as intermediate forms. Also exists in Ancient- (extinct) and Mythological types. Can have additional powers depending on the animal type.
Dr. Vegapunk's research has created a method to "feed" zoan type fruits to in-animate objects as well as a method to create artificial zoan fruits.
The most varied form of devil fruit, as all powers that don't fit into the above types are considered paramecia.