World

World is a supertype that is currently only found on enchantments. All existing cards with this supertype were printed as being 'Enchant World' cards.

From the Comprehensive Rules:

• 205.4d Any permanent with the supertype "world" is subject to the state-based effect for world permanents, also called the "world rule" (see rule 420.5i).
• 420.5i If two or more permanents have the supertype world, all except the one that has been a permanent with the world supertype in play for the shortest amount of time are put into their owners' graveyards. In the event of a tie for the shortest amount of time, all are put into their owners' graveyards. This is called the "world rule."