World file used by SMBX (Super Mario Bros. X), a fan-created clone of Super Mario Bros. for PC; saves the overhead map of a world, which includes paths to different playable levels (specified in .LVL files); can be customized using the Level Editor program included with SMBX.

Game file used by Terraria, a 2D action adventure and sandbox construction game; saves a world, which contains terrain, water, monsters, items, and other objects; used for single or multiplayer gameplay and can be loaded by the Terraria dedicated server, which allows players to host Terraria worlds over a network.

World files may be a pre-installed game map, or they may be a custom map created by the user. WLD files are saved to the following directory in Windows: [user]\Documents\My Games\Terraria\Worlds\. WLD files can be edited using the Terraria Map Editor (TEdit). They can be viewed without the Terraria game using MoreTerra (Terraria World Viewer).